Hi Bruce:
Ive been so many times to the central bank of Spain in Madrid for changing some pesetas to euros , never mind if theyre coins or banknotes, the only thing is that they have to be from 1939 to 2001 of that period of time.
So dont worry the 500 pesetas coins that you have theyre going to change you for euros without any problem.
if you have any other question, send me a PM i will respond you ASAP.
Regards,
Alfonso