Most people dont understand the amount of effort and expense it takes to put on an NSXPO and virtually no one understands legal implications. The NSXCA enters into legal contracts with these entities, procures insurance and has potential liability if "something goes wrong". We, as a club, have experience in managing these legalities but if you introduce non club members into the picture it could create legal issues not of our making but for which we could be responsible.
For example, at NSXPO 2006 two non-members showed up for the group photo at an air museum and then proceeded to do burnouts on museum property before driving recklessly onto public roads. The police were called and it took considerable amounts of schmoozing to avoid problems which we avoided only because I had photos of the cars and could prove they crashed the event and were not a part of our group.
I don't consider it to be "elitist" when the NSXCA has legal obligations pursuant to contracts and expends close to 6 figures to hold an NSXPO for our members. This is YOUR event and YOUR monies being used in conjunction with the generosity of our sponsors who do this each year for the NSXCA. There necessarily needs to be a "closed/private" aspect of the event for a multitude of reasons, all of which go to ensure that our paying members get the most positive experience we could possibly offer.