When it comes down to it, its not a huge leap to simply handle encounter and daily powers/slots like the vancian magic system: if you have the power you can choose to prepare it as many times as you want, assuming you have the slots for it.
As has been said, it will likely raise the PC power level - tho' only slightly I'd imagine - and it would potentially increase the repetitiveness of encounters, but I don't see it being glaringly game-breaking.
I've a player I often DM for who highly dislikes the 4E system mainly because of the at-will powers of spellcasters, and I've considered allowing him to swap those out for extra encounter/daily powers. He tends to be an old-school style caster player (only using spells when there is a genuine need, simply standing around and letting the fighters mop up otherwise) and doesn't much care for the idea of a caster having something to do every round. The situation isn't exactly the same (in this case I suspect dropping at-wills would make a PC weaker overall, but like 3E it would depend on how long you go between rests), but close enough.
As has been said, it will likely raise the PC power level - tho' only slightly I'd imagine - and it would potentially increase the repetitiveness of encounters, but I don't see it being glaringly game-breaking.
I've a player I often DM for who highly dislikes the 4E system mainly because of the at-will powers of spellcasters, and I've considered allowing him to swap those out for extra encounter/daily powers. He tends to be an old-school style caster player (only using spells when there is a genuine need, simply standing around and letting the fighters mop up otherwise) and doesn't much care for the idea of a caster having something to do every round. The situation isn't exactly the same (in this case I suspect dropping at-wills would make a PC weaker overall, but like 3E it would depend on how long you go between rests), but close enough.