Are there owners of these who use them?
Absolutely there are.
You have to remember that 99% of 432s and 432-Rs are still in Japan, and owners there, by their very nature (because it is a big commitment to own a classic car in Japan),
do tend to use the cars. There are very good informal local and national scenes as well as specialist clubs, and many events for them to attend.
A couple of friends of mine - one with a very well known 432-R, the other with a very well-travelled silver 432, clock up tens of thousands of km per year between them. The S20-engined cars are very practical, perfectly usable and a great 'package' for sporty driving. They don't need to be kept in glass boxes.