Excellent Topic My Friend!
Greetings!
mmadsen, I think your concept, prima facie, is just fine. I actually favor a lower-range magic level for at least most of the campaign or so.

In truth though, I like a good variety. In discussing this though, as *cool* as it is, I think there could be some serious problems with the de facto removal of the standard *howitzer model* wizard of D&D with a less ferocious, more subtly spell-equipped character.
Regardless of what name we want to give the class, or what type of magic the character accesses, or even what feats or skills the character enjoys, the problem does come up rather seriously with game balance.
*Hold On!*--you probably know me well enough to know that I'm not some super-high-fantasy reactionary munchkin or such, but what I mean is this:
The roster of monsters throughout the MM and their constituent populations is *intrinsically* geared towards the existance, dare I say, *proliferation* of the *Howitzer Model* wizards.
For a low-powered spell-caster to be effective, and even attractive for any PC, or even NPC, to take as a class the DM would have to orientate the entire monster-population and power level of the campaign.
For example, I used to play Warhammer Fantasy Roleplay. In several such campaigns, magic was powerful, but almost always low-key, and subtle. A +2 sword was very powerful, even rare, but didn't necessarily look like some great jewelled thing. And while useful, it was never game-unbalancing. Likewise, Wizard characters in the game were useful for adding subtle effects like attack bonuses and illusions, and light, and small bursts of flame for example, but wizards never became *Howitzer Models* In addition, while helpful, wizards weren't crucial to success. The opposition, which often consisted of humans, beastmen, orcs, brutish animals, trolls, skaven, and such, were almost never encountered in greater numbers than a dozen or two. In any event, the opponents could easily be killed with normal arrows, and other normal weaponry.
Because of the critical system, there wasn't really an "escalation" problem--i.e. Trolls and Orcs remained deadly regardless of how many careers your character had. Thus, there was no need to include an endless roster of ever more powerful and arcane monsters to challenge the party. That doesn't mean that different things were never encountered--just that the very power-level of the party didn't *demand* such.
Thus, with D&D now. Though many *balancing elements* exist, they are intrinsic to balancing towards the *Howitzer Model* Should a low-powered spell-caster work, the DM would be required to depopulate the campaign world significantly. Otherwise, the hordes of Wraiths, Drow, Demons, Beholders, Nightmares, and so on--you know the huge list--of magically powerful creatures would utterly destroy a party.
Now, one could do so--fix the campaign to accomodate such a low-powered spell-caster, but the world would require a lot of work on the dm's part, and the very operating dynamics of D&D would be challenged.
Semper Fidelis,
SHARK