When I design PrCs, I try to make the last level the "crown jewel" -- something really good to aim for, even if all the other abilities are just "flavor".
No offense, but a lot of your abilities are more than just "flavor", in fact the only one that is pure flavor is Attractiveness.
The fact of the matter is that if the sorceror gets bonus class skills from his DM, or uses non-core feats to gain certain skills as class skills, the sorceror can enter this class and outclass a regular sorceror in nearly every regard.
I find prerequisites to be a good limiting factor on prcs, limiting in that it prevents just anyone from taking them and it reveals the focus of the class immediately. A bard would have to spend some skills on good "spy" skills, take the "spy" negotiator feat, and then pick up one of 3 skills to get in. In other words, its a cake-walk for a bard, relatively speaking, whereas for the sorceror it is a royal pain.
A sorceror in the realms could take Cosmopolitan twice, and Negotiator once and spend a large number of skill points to get into this class, but could qualify by 6th level (Human Sorceror, Cosmo+Cosmo at 1st, Negotiator at 3rd, Spell Focus (Enchantment) at 6th). At that point it doesnt matter what the PC has given up because the next 10 levels are severely better than what they gave up. Picking up GSF (Enchantment) at 9th and riding this prc out gives the sorceror +3 DCs to all enchantments, +6 DCs to all mind-affecting enchantments vice a regualr sorceror. Also, quickening a 4th level enchantment is akin to turning a 4th level slot into an 8th level slot, and at 5 times per day that will see a LOT of use (abuse?). I mean tossing a quickened Crushing Despair before whatever other spell you are going to cast, for a sorceror or bard (who can't normally quicken), 5 times per day, at a DC at least +4 higher than a sorceror who took SF and GSF (Enchantment) - thats HUGE. Our human sorceror would also gain 2 sp/diplomancer level, the only thing missing (from almost all prcs) is the familiar progresison.
Granted, the sorceror in question gave up 2 feats (1st level feats) to pull it off, but as its possible such a sorceror would easily be a higher CR if an opponent, or in a party would outclass EVERYONE in social situations.
I think the prc needs to be reworked so great gains aren't balanced by steep prcs (for sorc only!). In this day and age I think something like Spellpower +1 (Enchantments only) would be better than something like Cloud Mind.
Technik