Looking through the modern systems that are coming out, whether they be more 'old school' or 'new school' there are a lot of ways to reward your players for various things. I mean, just going off the top of my head (and pulling from multiple systems) you have pushes, action points, drive points, void points, style points, hero points, fate points, force points, destiny points, dailies, rerolls, and the list could go on forever at times it feels. So, when do you know you have too much of a good thing?
A couple years ago (has it been that long already?) I was running a Star Wars game. Specifically Imperial Knights, but that is less important than that I was using a home-brew modification to an existing system (Roll and Keep from AEG's Legend of Five Rings) to run things. I felt the 'samurai' aspect of L5R would translate over well into Star Wars, and it didn't take much work to slap the Force on top of things. I'd already done gun combat rules for the system which also worked. However, despite home brewing the rules, there were aspects I liked about the D20 star wars, namely the Force Points you could spend for a major boost to important rolls. So I grabbed those.
I also liked rewarding players for being creative, doing recaps, and such like that so I gave Pushes out (basically something that lets you push a roll by 1 in any direction you want. Not much, but when you just barely fail it is nice to have). The power rules I had written for the Force also allowed for 'Force Surges' or moments when you truly delved deep into the force for a bit of an extra push to things.
See where this is going? Before I knew it the players had Void Points (just naturally from the system), Pushes, Force Surges, and Force Points, plus a generic once per session re-roll (replacing the Honor Roll mechanic from L5R 3rd ed). Sure I could keep up, and the seasoned L5R vets could, but for everyone else that is confusing. "I want this roll to work, so do I Force Surge, Void Point, Force Point, Re-Roll, Push, or some combination thereof?" Not to mention the differing levels of ability each had, from a push being able to add only a point to a roll, while a force point could add upwards of 4 keep 4 to the roll (that is roll and keep 4 additional dice when making the roll).
I had, simply put, gone too far with ways to reward the players. I should have cut out the Force Surge and Pushes at the very least. Rewards could've been done via Void points, and players would be left with 2 spendable things plus a reroll when times got dicey. Much easier to keep track of.
Basically what happened though is I was overly ambitious. In my desire to give the players more control over certain events I went too far and made a confusing scenario. So how far is too far? How much is too much? Honestly, I'd say the ideal spot is 2 or less "spendable" reward type things. There is no need for more, you have a lower power one that can be used for small rewards as well as whatever game mechanic they serve, and then a big one for the times when all the stops really need to be taken out for the act to succeed.
The Star Wars game was a success despite this, but I think it could've gone a bit faster if it wasn't for that confusion over all the things the players could spend. So, when making your own game (or adding things in) try to keep it reasonable with what you're adding. Everyone will be happier when there is less confusion going around the table.