[William Cloud Hicklin]

the bag of spare change that the Orcs threw at Thrór's companion: his beggar's fee, "a few coins of little worth". That insult would be quite lost if not both parties were familiar with the currency.

I don't think that's necessarily the case. If we assume, as I think we must, that the coinage of Middle-earth was like that of the Primary World up to the 20th century, coinage had intrinsic value, based on its composition: chiefly gold and silver, plus 'token' currency in copper, bronze, brass and sometimes iron. Note that Butterbur pays for Bill the Pony with "silver pennies," the standard circulating coin of the English middle ages (and 20 of them was considered a fair expense even for a prosperous innkeeper).

And much like Europe in the middle ages, coins we can assume spread far and wide beyond the land where they were minted, and quickly became a promiscuous mixture of origins. This didn't matter, since gold and silver were valued by weight anyway. So one didn't have to be "familiar with the currency" at all to tell that a 25-gram gold coin was of very substantial worth, or that a bag of small copper and brass pieces was of "little worth." Even today, it's apparent to most at a glance that a handful of faux-copper coins roughly the size of a US or European cent, Canadian penny or old German pfennig amounts to little, wherever they came from.