Again, I'm really worried about using at-will powers to recharge your mana pool. I'd recommend some other way of shortening combat instead, like damage to bloodied creatures being increased by 1/2 * level.
I like the expanded power selection rule. More options is good
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Here's how I'd do the mana system:
Encounter Mana Pool
Lvl 01: 4
Lvl 03: 5
Lvl 05: 6
Lvl 07: 7
Lvl 09: 8
Lvl 11: 10
Lvl 21: 11
Daily Mana Pool:
Level 01: 2
Level 02: 3
Level 05: 5
Level 06: 6
Level 09: 8
Level 10: 9
Level 12: 10
Level 16: 11
Level 20: 13
Level 22: 14
Level 26: 16
Encounter attack powers from your class (and PP/EP) cost 2 EMPs. Encounter utility powers from your class cost 1 EMP. Daily attack powers from your class cost 2 DMPs and 1 EMP. Daily utility powers from your class cost 1 DMP and 1 EMP. Encounter multiclass abilities cost 1 EMP. Daily multiclass abilities cost 1 DMP and 1 EMP.
Encounter item powers cost 1 EMP. Daily item powers cost 1 DMP and 1 EMP. Encounter racial powers beyond the first use cost 1 EMP. Daily racial abilities beyond the first use cost 1 DMP and 1 EMP. Powers gained as class features do not cost mana points. When you use a power or ability that costs mana points, you cannot use it again until the end of your next turn.
ETA: DMP can be used in place of EMP. EMP recovers after a short rest, DMP does not.
Once per encounter, you can take a standard action to expend a healing surge and regain no hit points. If you do, you gain 3 encounter mana points.
EDIT: changed some table stuff.
ETA: The hardest thing to balance is the amount of encounter mana points, since so many other things hook into it. At level 11, it basically translates to 4 encounter attack powers and 2x something elses, and at level 21 it's 4 encounter attack powers and 3x something elses. If you have lots of encounter utility powers, this mana system might actually reduce the amount of encounter powers you can use. Still, I'd think the greater flexibility will make up for that deficiency. In fact, the added flexibility might be too good, and the amount of encounter mana points may need to be reduced.
By the way, another bonus of this system is it limits novas. Spending all your daily powers in one combat means you lose 2 encounter attack powers that encounter.
ETA2: Another consideration is encounter utility powers that boost a skill. They should cost some other resource, otherwise they become too powerful. Maybe healing surges?
ETA3: If you allow Wizards to choose from any daily in their spellbook so they don't need to prepare half, would that be too powerful? That feat probably would be, but it could be changed to adding only 1 extra daily every time they pick it?