This seems like an interesting idea.
Place a restriction on how many healing surges a PC can spend outside of encounters. For instance, a PC can only spend two healing surges at the end of a short rest and they cannot take another short rest until they’ve had another encounter first.
In order to use their best abilities, the PCs need to build adrenaline or momentum or whatever you want to call it. Mechanically, it works like this: after an extended rest, a player only has access to one daily attack power – the lowest level one. After each encounter, during a short rest, he gains access to the next highest level one. If he has two powers of the same level, he can choose which one becomes available. The players can horde these powers or use them as they become available.
I don’t think I want to spring this on my players at this point. They’re heading for an aberrant castle, so I may mess around with some variant of this while they’re there. Currently I’m thinking that every encounter in a day bumps damage by a certain amount. The nice thing is that if it really doesn’t work it’ll only be for a certain set of encounters. I’m going to think about this some more.