Scrap the -10 to banned spells, that's a bad way to go about it. (Hmm, I'm going to focus on necromancy, which makes me a worse enchanter than when I started....what?) Instead, make banned schools cross-class skills.

Also, make everything spellcasting-related depend on the skill system, including spell slots per day. (Probably based on your highest school rank) Make school focus give something like +1 rank in that school's skill for each banned school. Scrap shadow evocation altogether. (it's a bad spell)

Make it so the wizard is a wizard basically because he gets all of the spell schools as class-skills, and gets an extra 4 points per level that can only go into them. (12 at level 1)

Now any class can practice magic the same way that a wizard does, only he'll be pretty bad at it, since the skills are cross-class.

The bard would get most or all spell schools as class skills, but no bonus skill-points to put in them, and no option to specialize.

No idea how the sorcerer would work.