I think I personally would prefer a system where most of the PCs' capabilities are in at-will and encounter resources (to make encounter balance easier, since the PCs will have approximately equal amounts of starting resources in each encounter), and daily resources that act as a sort of safety net to be pulled out in really tough encounters or encounters where the PCs have been very unlucky. Ideally, the daily abilities themselves should have some mechanism that discourages the players from "novaing" and encourages them to to save them for tough fights.
Healing spells, for example, could resore half of a character's lost hit points plus a random amount. Hence, they are most effective when used on a character who has lost most or all of his hit points.
Attack spells could have the option for the spellcaster to extend the casting time and "gather energy" for a greater effect. For example, fireball could deal just 2d6 damage if cast with no extra preparation. However, if the spellcaster gathers energy in the first round of a fight (this can be done in addition to casting an at-will spell), it could deal 3d6 damage if cast in the next round. If he continues to gather energy in the second round of the fight, it deals 4d6 damage in the third round. Attack spells thus get more effective the longer you spend casting them. This also makes successive castings of daily attack spells less effective since the spellcaster would have spent less or no time gathering energy for each spell.
Daily martial abilities (for those who want them) could have an extra boost that depends on how many hit points the user has lost to represent an increase in effectiveness from additional adrenaline.