Distance could matter, too. In the legend of Saint Dymphna, her father tracked her down when the innkeeper commented on his unusual coins -- and how he had seen them only once before.
Coinage was often important. Discovery of gold mines often heralded economic booms, because the increase in money supply facilitated trade; that, after all, is why money was invented in the first place. But it's kinda hard to use in stories except as local color, handing the characters a pile of disparate coins.
Though Poul Anderson did a little piece about fairy gold -- the money landed in a town where there were half a dozen people each of whom wanted to buy something and could afford it if only they could sell something. The gold worked its way about the town, and landed in the hands of the man who had originally gotten it before vanishing. And the ancient coins would make it obvious when characters found a treasure trove, even if -- or especially if -- they killed a dragon to do it. And coin exchange can be a nasty surprise if you are in far-off lands. . . .
Still, most of it is useful only for local color or minor hiccups in a novel.
