Spell levels are directly linked with character level (+- intelligence factor).]/quote]
Which is directly tied to experience.
I repeat myself, but trying to play in a "simulationist" way with a game using classes and levels is flawed. Try a skill-based game and let D&D be gamist.
I've refereed GURPS games. Heck, I used to use the GULLIVER variant. Skills are no less gamist than levels. Real world skills don't have nice discrete levels, nor do they hang around at high levels when they aren't regularly used. In fact, skill level is dependent on short, medium, and long term memory. Skills are tightly intertwined, so that its hard to get good at some things without being good at others, but simulating this results in an absurd number of complex skill defaults. Levels are just convienent bundles of skills.
But you are making an all or nothing argument. It's not that GURPS is pure simulationist and D20 is pure gamist. It's that D20 is slightly more gamist than GURPS. It is I think a very good balanced approach. To much more simulation makes game preparation too difficult. Too much less simulation, as we had in many areas of 1st edition, leads to alot of frustration with the systems inconsistancies, lack of internal non-gamist logic, and inability to handle situations not expressly covered by the rules. Frustration with the lack of internal consistancy and the unreality that rules encourage din player play was the reason I got out of AD&D. Third editions fix of those problems is the reason I left GURPS to come back to D&D. It now sounds like D&D is going backwards from my perspective.