MoonSong
Rules-lawyering drama queen but not a munchkin
I've had a very similar idea, and I think it makes a lot of sense. I particularly like the idea in combination with scalable spells, which scale depending on the slot you use to cast them.
Actually that seems to be a widespread idea over all. "Wandering slots" are part of my own houseruled 3.5: A wizard gains one spell slot every level until he has two of each level up to fifth level, where he maxes out at ten slots per day. Then as he gains access to more and more spell levels, the lower level slots migrate to the higher spell levels. And the spells variable effects and DC's are entirely reliant on the level of the slot, meaning that a fireball preppared on a third level slot has the same difficulty to be saved against and will deal the same damage regardless of the caster's INT and level. As a side effect a metamagicked fireball will always be weaker than a non-metamagicked one, but this is more of a feature than a bug.
But I must say I'm impressed WotC used the sam number of slots per level as I. (However I did choose two per level for entirely unrelated reasons, the most important, more than ten individual spells get unwieldy for my players)