Mark,
I'm guessing that if you tell them they can play an Open course that's had a green changed, a couple bunkers added and some mounding removed, they'll still come and play that, too, even if they can only play it at 6400 yards. But I'm not addressing the intelligence of the average American golfer, rather, I'm suggesting that this exercise is much ado about nothing that will ever be done, because the Links Trust and the R&A will continue to trot out the Old Course for the Open every chance they get, because it's great for business, much in the way that Pebble Beach wants to host the US Open every six or seven years. It's great for business. I doubt that they'd consider transforming Spyglass Hill so they could keep Pebble "pure" for the purists. I think a similar motivation exists for the Merions of the private club world in the US. They want to try to remain immortal in a sense of the word and the way they choose to seek it is to do whatever they have to do in order to host a US Open.
Contrarily, I don't think keeping a famous golf course as a sort of living museum is a good business model. I kind of like the idea since I'm fool enough to be seduced by the timelessness of such a concept, but I think there isn't a big enough market to keep a museum course open, unless, of course, it is subsidized by the government.