Wow. This is awesome. You un-broke the broken. Very cool.
This reminds me of what I just finished doing to the wizard class:
Wizards gain spell points per level equal to: 5+INT modifier + WIS Modifier x 2
A wizard with +4 INT and +4 WIS would gain eighteen points per level.
A wizard starts knowing all Cantrip spells.
In order to learn spells from a certain school a wizard would have to spend his accumulated spell points to learn a spell level in a certain area of magic. I.E. A wizard would have to spend 25 of his spell points to open up the possibility of learning 4th level evocation spells.
The goal of this point system is to force the wizard to be more specialized if he ever wants to gain access to all of the high level spells, but allows a wizard to also choose to become more generalized and get to only medium level spells in several different spell areas.
Evocation, Transmutation, Conjuration, Abjuration, Divination, Illusion, Death
This is not effected, nor does it have any effect, upon the wizards spells per day list. The spells per day list only shows how many spells a wizard could cast 'if' he had access to that level of spells. If he does not have access to that level of spells then he can not cast that level of spells. And of course a wizard who reaches 9th level spells in Divination would have access to all the spells per day up to 9th for divination spells, but would be unable to cast 9th level Transmutation spells unless he also had reached 9th level in that field as well.
A wizard may bypass this by finding an alternate means of learning spells, (other then the traditional method of studying).
For instance a wizard could be taught a spell from a different field of magic by another wizard who was willing to teach that spell. Or the Wizard might learn a new spell from an ancient spell book if he takes the time to sit down and figure it out. Of course even if he is taught a spell he must be able to cast that spell on his spells per day chart.
Also a wizard may not automatically learn spells just because he gains access to that field of magic. When a wizard learns a new field of magic, he gains one 'free' spell, from the field of magic which he has just learned, which he may place in his spellbook. A wizard must find a source of learning to actually learn new spells. (I.E. Another wizard, a library, ancient scrolls etc.) This means that to learn all possible spells a wizard must actually spend time seeking out all possible sources of magic. Some fellow wizards might be unwilling to teach certain spells that they themselves spent much time learning, dragons are unlikely to part with the ancient tomes of knowledge and priests are sure to have hidden the secrets of the 'unnatural' Arcane magic away in secret vaults. The search for magic will not be easy.
I like the fact that it allows for more customization, and makes the Sorcerer a playable class once again. (I took it out of my campaign setting becuase it was simply too broken and i didn't know how to fix it.)
All in all I have to say excellent work and... can I use this idea in my campaign setting if I credit you?