I would like to comment not so much on the coin but rather on one comment.
Quote:
It wouldn't seem to be terribly profitable to counterfeit these, either when they were circulating or as a very modestly priced collectible in the present day,...
That is often the prevailing opinion but it is incorrect. This coin is not a contemporary circulating counterfeit because it is actually too nice a design to have been produced without transfer. However, in 1752 a silver 1/2 reale was a lot of money. Remember hundreds of industrious counterfeiters were making halfpennies and farthings at that time.
In the 1850s there were Mexican 1/4 reales made for circulation and 1/2 reales were VERY numerous.
In 1893 there was a plague of counterfeit US cents.
In the 1950s Francis Henning made money forging nickels.
As a Numismatic forgery - the profits are much higher. The cost to make a 1/2 reale using a transfer die would be far less than 10 cents and the result would sell for $10.
So never believe a coin would not be counterfeited because it was of too little a value. If the coin is made it is forged.