Quote:
... A membership-supported theme museum in rural, central Pennsylvania doesn't seem remotely possible. Is this a "must do" travel destination for anyone ...
That is a fair question, bookbndrbob, and here's another:
Q/ If we built the Federal Reserve system today, would five of the twelve banks be in Philadelphia, Cleveland, Richmond, St Louis, and Kansas City?
The answer to both your question & mine lies in the geography of 1886, not 2016.
Very few of us could do a good job listing the largest and/or most important American cities of 1886 but, if you google-up such a list, you'll probably find that "rural, central Pennsylvania" is smack in the middle of the lot.
Cities that "we" barely think of today - Cincinnati, Buffalo, etc - were Much Bigger Deals in 1886, while cities that are important today - Los Angeles, Houston, Orlando, etc - were but gleams in their City Fathers' eyes.
I suggest that you take-up collecting postcards of The Golden Era to better appreciate The Way Things Were

Lastly, the future of
any "member-supported theme museum" may have less to do with physical visitors and more to do with their online gift store, branded debit cards, member-targeted travel packages ... kinda like the AARP.
The Turner Movie Channel does movie-lover ocean cruises, on which I doubt they lose money.
Q/ How about an Official APS Philatelic Tour of the UK? Plenty of places to visit ...
Cheers,
/s/ ikeyPikey
Edited to Add: The APS was founded in 1886, but the Bellafonte location was decided upon in the early 1940s. The Fed was founded in 1913.