The total number of NSXprime members is shown on the main page for the Forums. As of this writing it's 2,850.
What percentage of NSXprime members own NSXs? Any of us could make a guess. You could check out
Lud's previous polls for some clues. Poll number 5 implies that 68 percent of NSXprime members are NSX owners, but that's only if - and it's a BIG "if" - those responding to the poll are representative of those not voting, and if they're telling the truth. Poll number 8 implies that at least 1368 of the members are NSX owners.
Also keep in mind that NSXprime is primarily, but NOT exclusively, skewed towards North America. Approximately 8,000 NSXs have been sold in the United States, roughly 800 in Canada, roughly 8,000 in Japan, 1,500 in Europe, and another 1-2K scattered around the rest of the world. So totals of NSXprime owners include some folks in these other markets, and any estimation of the percentage of owners ought to take into account the geographical distribution of cars and of NSXprime members. In figuring out what percentage of owners are here, you can't limit yourself to the number of cars sold in the United States but include all NSXprime members including those living in other countries.
And, of course, just because someone is signed up as an NSXprime member, doesn't mean that they come here frequently, or even at all. And there may be folks who are NSX owners who don't register as NSXprime members but still stop in from time to time.