....
What I would like to know is whether or not any foreign governments actually
give a flier about US yachts using vhf radios in their waters. I suspect the
answer is "no, not really." ...

I've checked into an even dozen different foreign countries, most of
them two or three times and never had anyone check my radio licenses.
YMMV, and they are required so having them is the right thing to do.

-- Tom.