I like the idea of Coins myself, I feel like they bring balance to things but give you some unique opportunities. One interesting twist could be special access to a rich resource world for a limited period of time, perhaps based upon how many coins you choose to use.
I’ve liked the idea of the ability to use Coins to fly for brief periods of time, but I also wouldn’t mind having the ability to trade in amounts of coins for certain things, such as customized creature spawners (Like I have wanted to build an automated cattle farm) or having ones already in the world moved. Another interesting idea would be the ability to have our region’s biome changed.
Mob disguise is one of those things I’d bribe someone to have access to.
I also like the ability to gain access to some things that are normally restricted, such as larger regions.