Well, for one thing, there's no reason to lower the LA adjustment for divine spellcasting, because it's not inherantly weaker than arcane, just more focused. Sure, it's not as suited to blasting, but it's mostly superior for buffing (barring polymorphing, which doesn't kick in until the middle levels, and still has shortcomings and difficulties), and it's far better for healing and necromancy.
The cleric and druid classes get better stats and goodies than mages only because the designers want people to play divine casters for the sake of providing the group with a healer. Not because they're inferior to mages otherwise. A caveat to that is that druids have a much more limited spell list than others in terms of versatility and raw power (though not in all departments; some of their spells are just as powerful, but many aren't; they get most Cure spells at later levels, for example). So it's possible that druid spellcasting may be slightly inferior to wizard/sorcerer and cleric spellcasting. Still, probably not enough so to be worth a different Level Adjustment.
Secondly, you don't address the fact that bards, druids, paladins, and (maybe) rangers have access to some unique spells, such as Sculpt Sound, Modify Memory, Holy Sword, Spellstaff, Produce Flame, etc. You don't even mention druid spellcasting as an option. Also, you don't address cleric Domains; would taking the cleric spellcasting grant a character 2 domains and their granted powers? And would it provide them the spontaneous Cure or Inflict spells of a cleric?
Also, note that clerics get Turning/Rebuking for a reason; evil clerics in particular won't be able to control much in the way of undead without it. The Create Undead and Create Greater Undead spells, for example, don't grant any kind of control over the undead created; it's expected that the character will just Rebuke those undead as they form (while arcane casters might be able to do something with Command Undead or Control Undead spells, but that's less timely and may get the mage killed by his undead creations before he can even begin casting the extra spell).
So at least provide the undead turning or rebuking capacity as feat choices. Most likely, the first such feat would only allow turning or rebuking 1/day + Charisma modifier, as per a character of their level, and it would probably require spellcasting ability from the cleric list. Extra Turning feats could be taken afterward if needed.
Third, the level adjustment should really be based on their actual level, not just a static value. +4 LA at 1st-level will suck HORRIBLY, especially with just measly 1st-level spells in exchange. A fighter does 2-3 times more damage than them and a rogue can do most of the utility stuff as well or better than a 1st-level caster.
My Sunday night game has a lesser lizardman character (called Saurians) with a +1 LA, a half-dragon elf with a +3 LA if I recall correctly, a human, an elf, and a vanara. The saurian is ECL 3 now, as a 2nd-level Dragon Shaman, and he's far tougher than the half-dragon, far more useful to the party, and almost equal in offensive ability (arguably better since his Power Aura can boost the whole group's melee damage by +1). The vanara cleric (3rd-level) and human soulknife (3rd-level) are tougher too, with more class feature goodies, and similar damage output or healing output on par with it. The elven sorceress is more accurate with her spells and has more utility.
The half-dragon? Well, he's still a 1st-level ranger with nothing but a 1/day breath weapon going for him. Sure, his AC is just a few points shy of the saurian's, and his HP is slightly better than the 2nd-level elf sorcerer's, but he gets beaten within an inch of his life all the time, and can only outperform the others once per day with a line of acid breath weapon (which, while effective, is basically a one-enemy knockout attack). His Strength is slightly higher than the saurian's but his lack of extra BAB, feats, or class features makes that fairly irrelevant so far.
Anyway, the LA should vary with character level. At 1st-level, it's worth no more than a +1 LA. Once they reach 5th-level it may be a +2 LA. At 9th it may be a +3 LA. At 13th it may be a +4 LA. At 17th it may be a +5 LA. This might be a bit off (it may be more like +2 at 5th (definitely not at 3rd, as the first +1 LA overcompensates for mere 1st and 0-level spells), +3 at 7th, +4 at 9th, +5 at 11th, +6 at 13th, +7 at 15th, +8 at 17th, and +9 at 19th).
Another point, you have to make spellcasting-related skills available as class skills, preferably not just to the Expert NPC class. Either make this part of the spellcasting LA benefits, or make a feat called something like Magic Student, that makes Concentration, Knowledge (arcana), and Spellcraft into class skills for the character.
