I don't think the two (magic power source and currency) are mutually exclusive.

If you've got a sufficiently magical society, it could easily be the case that how rich and powerful you are is based on how much magic power you have... which is represented by how many of these coins you have lying around. Currencies are/were based on some standard, and using the value of some quantum of magical power seems as good as basing it on the value of a pound of silver.

This then raises questions like whether there is a finite amount of magical power, why the star-chasers are the only ones who can tap into it to put it into the coins, and why constantly making new coins doesn't lead to inflation if the existing ones are indestructible and rechargeable (not sure if they were still valuable when they were discharged).

Not insurmountable questions, but something to think about.