That's pretty much what 4e did (cleric: buff/radiant/healing, wizard: area/elemental/debuff, etc) but I think (and have thought for a while) that clerics, druids and wizards need to go and be replaced by mystics, spirit shamans*, and sorcerers; small customized list of spells with lots of uses per day.
It would fix swiss-army wizards having "just the spell" for everything.
It would fix "24 hours later, Bob is no longer diseased, cursed, and missing a limb" healing.
It would go a long way to correct 15 minute workdays (esp when you have 7-8 spells per spell level per day).
It would go a long way toward item creation-bots who have wands and scrolls of utility magic for nearly any problem and can make any magic item in the game.
It would make caster spell choice come at level up (where every other class makes its choices), not at point of rest where they can rebuild themselves to "properly handle" (read dominate) the challenges. (All fire spells in the Ice Temple)
It would make for more thematic casters (healers, illusionists, necromancers, fire-mages)
In short, I think it would fix 90% of 3.X's problem with casters.
* Though the spirit shaman doesn't work like the other spontaneous casters. Perhaps a different spontaneous druid-spell caster class would work better.