A bump, and a contribution.
A First Look at the Classes:
Barbarians have a wild, primal appeal that can be reflected by giving them freely the Powerful Lover trick.
Bards enjoy using their artistic performances for good effects. They have new Bardic Music effects. Furthermore, characters who have 5 ranks or more in Perform and have chosen Erotic Arts as one of their Perform style get a +2 synergy bonus on their Sexual Prowess rolls.
Clerics rely on their spells for carnal arts.
Druids have, like clerics, access to several useful spells. In addition, their exhaustive knowledge of all natural things allows them to tell whether a partner is infected by a venerian disease; and they get the Resist Disease trick for free.
Fighters focalize on martial training. Their class don't give them special capacities in the bedroom arts.
Monks try to achieve physical perfection. Most monks forsake all sexual activities, channeling their sexual energy to put it to other uses. But those monks that do not renounce sex make excellent lovers. Monks get the Insightful Lover for free, and furthermore they gain an additional insight bonus equal to one-fifth (rounded down) their monk level to their Sexual Prowess roll reflecting their mastery over their body. Finally, at 5th level, male monks get Quick Recovery while female monks get Muscular Control for free.
Paladins, like monks, often voluntarily choose to forsake sexual activities; but those that do not find new uses to their rigorous training. Paladins can tap the litteral power of love, and their Lay on Hand and Remove Disease abilities are strengthened when they use them during sex with a partner they truly love. Lay on hands used this way cured twice the normal amount of hit points; and they can use the remove disease spell-like ability one additional times per week in this same way.
Psions and Psychic Warriors learn to develop their innate supernatural powers. Forcing their body to obey to their will, they can practice minor effects that enhance the sexual experience. These effects give them a circumstance bonus to their Sexual Prowess roll equals to the highest level of power they can actually manifest (a 17th-level psion whose Power Point reserve has been reduced to 5 by extensive manifestation will get a +3 circumstance bonus, but once having recovered all his power points, he would get a +8 circumstance bonus).
Rangers' lifestyle lend them to loneliness. Their class features, centered on combat and survival, don't give much in the field of love -- except noxious snickering about their relationship with their animal companions...
Rogues are, of all adventurers, the ones that spend the most time learning the subtleties of anatomy and the location of the most sensitive nerves. They usually use this knowledge in combat, hitting where it hurts the most, striking vital or sensitive organs to maximize damage or pain and put their foes out of combat quickly. But they can use this anatomical lore for pleasure rather than pain; and get a +1 bonus per sneak attack die they can inflict in combat to their Sexual Prowess rolls. The primary function of this training being to hurt, however, sadistic rogues (i.e., those having the Sadic sex trick) get a +2 synergy bonus in addition.
Sorcerers wield an innate, intuitive magic. Like psions and psychic warriors, this allows them to cast minor magical effects during love, which grant them a circumstance bonus equal to the highest spell level they can actually cast.
Wizards don't enjoy the intuitive grasp of magic that sorcerers know; but more than largely compensate by being able to research, prepare and cast erotic spells that most sorcerers can't afford to master, needing to concentrate on more general-purpose spells.
Note on Familiars: Familiars are extensions of their master's being. Master and familiar are, for all purpose, one and the same being. People would thus not be surprised to know that when two mages make love, their familiars imitate them as they can. If both are sexually compatible and of opposite sex, they will make love; otherwise they will merely sensually caress each other.
Adepts, like clerics and druids, have an exhaustive list of spells at their disposal. The level 1--5 spells of the Midwifery domain are also on the adepts' list; as they frequently serve as midwife.
Aristocrats, it's a staple of fantasy, are usually lovely; beautiful and regal. They freely get the Smooth Lover trick since first level.
Commoners, by definition average to the point of mediocrity, don't enjoy anything special they could use in bedroom -- or anywhere else, for that matter.
Experts, like all classes, get Sexual Prowess freely as a class skill. However, experts who explicitely choose Sexual Prowess as one of their class skills are considered to have a Sexual Prowess Rank two points higher than their actual score for the purpose of trick prerequisite. Furthermore, they get two bonus sex tricks they can choose freely among those for which they qualify.
Warriors, like fighters, have no special training in the carnal sport and get no special benefit.
Some new sex trick proposals. Some are just variations of existing ones that I felt missing (at least from the 0.5 version available on the site); but not all.
Insatiable Lover
Prerequisites: 10 Ranks Sexual Prowess, Enduring Lover, Intuitive Lover, Spiritual Lover, Tantric Lore, Tireless Lover
Benefits: You can never have two much. You get a +6 resistance bonus to your Arousal check. This overlaps (does not stack with) the +4 resistance bonus from Tantric Lore. You can choose to apply or not this bonus at will. When you do, you can also confer a +3 resistance bonus to your partner, reflecting the experience you have at teasing partners to prolongate intercourses. Additionally, if you are male and have the Quick Recovery trick, you get a +5 bonus on your Recovery check.
Lover Focus
Prerequisites: 4 Ranks Sexual Prowess, Intuitive Lover, must have had at least weekly intercourses with the same lovers for at least one whole year
Benefits: You know your lover's body nearly as much as your own. You gain a +5 competence bonus on Sexual Prowess rolls and Arousal checks related to that partner.
You may take this trick multiple times, each time selecting another partner.
Penetration Focus
Prerequisite: 5 Ranks Sexual Prowess, Dexterous Lover, Enduring Lover, must be male
Benefits: You are expert in thrusting rythms and movements, knowing how to intensify your partner's sensation and avoid inflicting pain.
You gain a +1 bonus to your Sexual Prowess checks when penetrating. You may take this trick multiple times, increasing your bonus by +1 with each instance.
Phalic Focus
Prerequisites: 3 Ranks Sexual Prowess, Intuitive Lover
Benefits: When stimulating your partner’s phalus, you gain a +1 competence bonus to your Sexual Prowess Checks. You may take this trick multiple times, increasing your bonus by +1 with each instance.
Tireless Lover
Prerequisites: 5 Ranks Sexual Prowess, Enduring Lover, Con 14+
Benefits: When using Constitution as your relevant ability for Sexual Prowess checks, you may add 1.5 times your Constitution modifier to the check.
Psychic Link 1 (Psionic Trick)
Prerequisites: 6 Ranks Sexual Prowess, at least one telepathic power known, Reserve Power Points 5+
Benefits: You are able to project your sensations to your lover's mind during an intercourse. Your lover needs to make Arousal Checks against both your Sexual Prowess rolls and his or her very own. This trick is spell-like in nature and may be resisted by a Will Save (DC 10 + your Charisma modifier + half your manifester level) and Spell Resistance apply. You can use this trick on only one lover at once.
Psychic Link 2 (Psionic Trick)
Prerequisite: 10 Ranks Sexual Prowess, Psychic Link 1, Reserve Power Points 11+
Benefits: You are now also able to feel your lover's sensations during an intercourse. This is used in conjunction with Psychic Link 1. You need to make Arousal checks against both your lover's Sexual Prowess rolls and your very own.
Vaginal Focus
Prerequisites: 3 Ranks Sexual Prowess, Intuitive Lover
Benefits: When stimulating your partner’s vagina, you gain a +1 competence bonus to your Sexual Prowess Checks. You may take this trick multiple times, increasing your bonus by +1 with each instance.
Versatile Lover
Prerequisite: 7 ranks Sexual Prowess, at least two tricks among Creative Lover, Dexterous Lover, Enduring Lover, Intuitive Lover, and Powerful Lover
Benefit: You gain a +1 synergy bonus for each trick you know among Creative Lover, Dexterous Lover, Enduring Lover, Forceful Lover, Intuitive Lover, Inventive Lover, Powerful Lover, Smooth Lover, Spiritual Lover, Tireless Lover, and Wild Lover
Maybe it's too late to add new feats (since the feat and spell document is called "endversion"), but here are three new feats nonetheless. Actually, only two since one is in fact twined for psionic purposes. Actually only one and a half, since the other is just a variation on Iron Celibacy.
Iron Fidelity [General]
Prerequisites: Wis 15, must have had exclusive relationship with one lover for at least one year
You are permanently immune to any seduction based effect including those of Sucubbi, Nymphs and various sex-related magics and feats. This feat is rendered useless for a year if you engage in any voluntary adultery. If you engage in voluntary adultery within that year the feat is rendered useless permanently.
Union-Cast Spell [Metamagic]
You can extend an union of the flesh to more mystical ranges, allowing you to cast spells that affects both you and your partner during sex.
Prerequisite: Aroused Casting, Sexual Prowess skill
Benefit: You can cast a personal or touch spell that normally affects only person on both you and your partner during sex. (In case of multiple partners, only one of your chosing is affected.) Both you and your partner receive the full effect of the spell (for example, a cure light wound spell cast at 5th level would heal 1d8+5 hit points on both you and your partner). Even spells that are normally self only would work on both. The same spell apply on both characters, so variable, numerical values are rolled only once (so in the cure light wound example, if you roll a 6, both you and your partner would be healed 11 hp) and effects that must be chosen at the time of casting are similar for both characters (so, if you cast polymorph self this way to turn into a giant eagle, both you and your partner would become giant eagles). If a spell is dispelled or dismissed on one partner, the spell is similarly canceled on the other. Finally, for the whole duration of a non-instantaneous spell, both you or your partner can make a Scry check (DC 25 minus spell level) to intuit the distance and direction of the other recipient of the spell, as the mystical union is maintained.
An union-cast spell uses up a spell slot two levels higher than the spell's normal level, modified by any other metamagic feats.
Union-Manifested Power [Metamagic]
You can extend an union of the flesh to more metaphysical ranges, allowing you to manifest powers that affects both you and your partner during sex.
Prerequisite: Erotic Manifestation, Sexual Prowess skill
Benefit: You can manifest a personal or touch power that normally affects only person on both you and your partner during sex. (In case of multiple partners, only one of your chosing is affected.) Both you and your partner receive the full effect of the power (for example, a lesser body adjustment power manifested to heal would heal 1d8 hit points on both you and your partner). Even powers that are normally self only would work on both. The same power apply on both characters, so variable, numerical values are rolled only once (so in the lesser body adjustment example, if you roll a 6, both you and your partner would be healed 6 hp) and effects that must be chosen at the time of manifesting are similar for both characters (so, if you manifest polymorph self this way to turn into a giant eagle, both you and your partner would become giant eagles). If the power is negated or dismissed on one partner, the power is similarly canceled on the other. Finally, for the whole duration of a non-instantaneous power, both you or your partner can make a Remote View check (DC 25 minus power level) to intuit the distance and direction of the other recipient of the spell, as the metaphysical union is maintained.
An union-manifested power costs a number of power points equal to its standard cost + 4, modified by any other metapsionic feats.