I was thinking along a similar line recently.
First, I'd make spell slots count only for spells that you want to cast in combat. I'd make everything else an expensive, slow ritual, including some things like
Overland Teleport. That's to help the LFQW problem.
Secondly, they've already got a Feat to have an At-Will spell for lower levels. (Which I approve of heartily.) I'd also give higher-level casters lower level At Wills for free. This is to offset...
Third: Ditch the old tables with a zillion spells/day. You get 3 + Ability Mod preparable First level slots to start with. (Not sure yet how I'd handle multi-classers.

) As you go up in level, these slots increase in their ability to handle higher level spells. I'm often a DM, and 3e taught me to hate filling out spell charts for high-level caster NPCs. (2e should have, as well, but I was younger then.

) You are, of course, free to prepare a spell in a slot at a lower level than the maximum allowed.
Code:
[B]
Caster Slot - Maximum level of spell held
Lev 1 2 3 4 5 6 7 8 9 10[/B]
1 1 1 1 1* 1* 1* 1* 1* 1* 1*
2 1 1 1 1 1* 1* 1* 1* 1* 1*
3 2 1 1 1 1 1* 1* 1* 1* 1*
4 2 2 1 1 1 1 1* 1* 1* 1*
5 3 2 2 1 1 1 1 1* 1* 1*
6 3 3 2 2 1 1 1 1 1* 1*
7 4 3 3 2 2 1 1 1 1 1*
8 4 4 3 3 2 2 1 1 1 1
9 5 4 4 3 3 2 2 1 1 1
10 5 5 4 4 3 3 2 2 1 1
11 6 5 5 4 4 3 3 2 2 1
12 6 6 5 5 4 4 3 3 2 2
13 7 6 6 5 5 4 4 3 3 2
14 7 7 6 6 5 5 4 4 3 3
15 8 7 7 6 6 5 5 4 4 3
16 8 8 7 7 6 6 5 5 4 4
17 9 8 8 7 7 6 6 5 5 4
18 9 9 8 8 7 7 6 6 5 5
19 9 9 9 8 8 7 7 6 6 5
20 9 9 9 9 8 8 7 7 6 6
*Limited by 3+Ability Mod slots
As a spell level "drops off" the chart, gain
an "At Will" spell prepared at that level.
The chart above keeps the same "highest level spell you can cast" from previous editions. To reduce ability score dependence, the slots level up from the "front", so higher ability scores lets you retain a few extra slots of lower level. This makes high-ability scores more useful at lower levels, but drops off that utility as the game progresses.
Writing that chart out Old-School fashion:
Code:
Old School Progression
Max Spells at Level
Caster
Lev 1 2 3 4 5 6 7 8 9
1 4* 0 0 0 0 0 0 0 0
2 4* 0 0 0 0 0 0 0 0
3 4* 1 0 0 0 0 0 0 0
4 4* 2 0 0 0 0 0 0 0
5 4* 2 1 0 0 0 0 0 0
6 4* 2 2 0 0 0 0 0 0
7 4* 2 2 1 0 0 0 0 0
8 4 2 2 2 0 0 0 0 0
9 3 2 2 2 1 0 0 0 0
10 2 2 2 2 2 0 0 0 0
11 1 2 2 2 2 1 0 0 0
12 W 2 2 2 2 2 0 0 0
13 W 1 2 2 2 2 1 0 0
14 W W 2 2 2 2 2 0 0
15 W W 1 2 2 2 2 1 0
16 W W W 2 2 2 2 2 0
17 W W W 1 2 2 2 2 1
18 W W W W 2 2 2 2 2
19 W W W W 1 2 2 2 3
20 W W W W W 2 2 2 4
*Limited by 3 + Ability Modifier
W = an At Will spell of that level
Even a 20th level caster has only 15 slots to fill: 4@9th, 2 each at 8th, 7th, and 6th, and "At Will" slots of 1st through 5th. (Although he may also have additional At-Wills through feats.
Anyway, that's how I'm thinking at the moment.