The copper and platinum pieces are all worth 1gp and are treated as items separate from the 'proper' currency though, lol.
I really do think it might be better to just move to a copper-based currency with the other denominations serving for powers of ten values of copper pieces. A lot of games, particularly rpgs do this sort of thing-have 2 copper pieces, pick up 9 copper pieces, now you have 1 silver piece and 1 copper piece, etc.
It could also iron out some of the economical oddities-a lot of items would be ridiculously overpriced even at even at 1gp...a value which is essentially worthless in game. You can essentially become rich beyond a commoner's dreams by stealing all the plates and forks out of some poor fools pantry, at the same time that gp doesn't get you very far in this game. Using cp as a base would allow some more nuance into a system that currently has you paying for apples with the equivalent of hundred-dollar bills, while giving a greater range for items to be valued in.
