I wonder whether an over-abundance of gold or other coins could lead to people using the gold for other purposes (such as magical reagents). I don't know enough about how real world inflation works to speculate about how the fantasy version would work.

I remember roughly a decade ago I worked out that a gold was equivalent in purchasing power to somewhere on the order of $100, and $100 was a nice round number that’s easy to use to get a ballpark feel for what something is worth, so I pretty much always use that. I’m guessing inflation and/or doomsday preppers (or political culture) has significantly raised the price of gold since then. Inflation too.