I only got a few min, but these are all great! This is why I brought it here, to beat out all these things I never would of thought of. I only argue against your questions (in favor of the idea) so I can provoke more questions, I still don't know if I want the Gem/Coin, it would be way exciting to get it to fit but we'll see!

For the Metal, the Kingdom that created them in the first place, inscribed certain patterns along the coins, that would be recognized as a symbol. The symbol would be in connection with a natural force, lets say fire for example. One of the other powers of the gem was to create beings of that natural force. So for our example the leaders and those who knew how to use these other powers, could now run around without anyone really knowing how these things of legend (beings of fire) were being created because they held these coins that everyone had. Theres a bit more to that, but thats the basic idea...

Now onto the whole splurging or hoarding idea, it would be perfect for the Star-Chasers to regulate how much is actually out there, if people Hoard them, then they can have an high exchange rate to get them back or something, I'm sure there can be other ways to regulate but just a thought.

290blue, that was the premise I was going on, those who could control stronger amounts of the Gem, or even 2 different infusions of the Gems would be the nobility of this area. The world will always have an abundance of the magical power, but people have a finite amount of power they can draw out of the gems, that amount can be increased based on several things though. The Star-Chasers are the only ones who have the ability to draw power into the Gems (haven't decided how that ability is received though)

But I guess I should clarify the Gems are indestructible not the Coins themselves, but inflation was another issue I thought of, but still don't have a real answer for, other then the regulations I mentioned above from the Star-Chasers (the continents currency society haha)...