Trading currency

I just started playing and am enjoying the app but my main gripe is the currency used for trading. I understand putting the timer on it, that's fine. But then the currency itself is overkill. It isn't enough for me to stop playing but I can see it getting annoying enough times that I say "screw it" and uninstall.

A change that would make sense is that it's used to trade up in rarity.

Either way, this is just my frustration.