See on one hand you have them as currency, and on the other hand they are some kind of power source for magic...
Either they will end up useless as currency (because people will hoarde them or splurge them recklessly depending on their magic value) or they will end up useless as a magic-power-item (because people will hoarde them or splurge them recklessly because they are useless as coinage).

Trying to make it a doubly-useful object (by incorporating magic items) seems like you're going to destine it to fail as the other.

I'm all for arcane counterfeit protection, for magical formation of currency or even the use of currency within magic... but I don't see a merging of the two aspects into a "magical power coin" being very feasible in a larger world.