Speaking of RMM's, I've been trying to get the 'there is a universal currency, each player at any point has some amount of $ (which is unknown to him), each player can request (almost) any power, and if he has enough $, it happens, if not, nothing happens' idea to work by making a sheet of all powers, but it's impossible... there are so many, and some actions scale depending on whether or not not they're self-targeted, or depending on alignment or ingame day, and some don't, etc.
There is a way to make it work, which is by having me decide how much something costs upon submission, the question is just is that something players would want to play, as there is an element of mod capriciousness (I had to look that word up), which is generally considered bastard. I would try to keep it at a minimum, by a) setting some guidelines beforehand, b) writing down every action I price and comparing them, and c) hiding players currency from myself, so that I never know whether or not it's affordable -- but I can't eliminate it completely.