Adventurers should use another type of currency
I think it's rather ridiculous that an adventurer can go around the world and in a few years become wealthier than any landed monarch, and then they can just take some land over and suddenly they are the wealthiest monarch in the world.
Since the game supports different types of currencies, how about Adventurers use Silver instead of Gold, to represent the fact that they are on a lower scale of wealth?
If they ever got landed, you could make a 20:1 conversion to gold or something like that.