Game Builder's Block

I have been trying to write SkyRPG this week.  I have all kinds of ideas about writing a good fantasy RPG but there is one problem I have been finding especially thorny.  I am trying to figure out how character powers should work and no matter how I twist it about I can't find a solution that makes me smile.  The classic DnD style is that fighters do exactly the same thing every round and can do it forever while mages have all kinds of options and eventually are flat out unable to contribute.  I don't like either of those options much.  In 4th edition DnD the system is much better since everyone gets a variety of abilities but I am not sold on the concept of everybody using a predictable series of strong abilities and then petering out at the end.

My challenge is that there are some fundamental constraints on power design.  If you give players variable power in their abilities they will always choose to use the most powerful abilities first to blow up the enemies as rapidly as possible and leave as little as possible for later.  I can't think of a design strategy where it would be optimal to do anything but use the biggest guns first - aside from making all the really good powers highly situational which feels very strange to me.  There are a number of ways to gate player power from having magic points that can run out to simply having powers only be usable once per fight but either way if you let people frontload their big moves they inevitably will.

The other constraint is that if you don't allow players to alter the power of their actions they won't necessarily feel like they have a lot of control over fights.  Also it would imply having a pretty tight balance on various abilities because if your balance is way off then you pretty much end up with the first problem of everyone just using the overpowered abilities first (or exclusively).  I have tried to set up systems where all of the player's abilities are equal but it is really a struggle to hit that mark and even if I do hit it I don't know that I like the result much.

The ideal, from a theoretical perspective, is some sort of variable cost system with regeneration.  If characters spent points to use abilities and slowly regenerate them it is possible to prevent frontloading of big powers and also provide flexibility and options in combat.  The thing I constantly struggle with is the complexity of managing point systems that have regeneration.  I don't think people are particularly happy about recording points spent and the values either need to be really big or the granularity is really low.  Going from regenerating two points a turn to three points a turn.

I am well and truly blocked.