Wojtek, what a great "seed" for thought!! I hope my ideas that follow are worthy...
I had a brief stint in radio, and played a lot of prog. This was the early 90s, and the genre was really disdained at the time, and the station played predominantly obscure "alt rock", post-punk, etc. However, I was appreciated (by some) for my own take on "obscure".
I became privy to a conversation about my show that went something like this:
DJ 1 to ProgDIr: "What does that guy Alaric play?"
ProgDir: "It's mostly people with chops!"
DJ 2 to both: "Yeah, it's the 'People With Chops Show!'"
(OK, I'm proud of that!

)
But, my point is that prog music is (to me... uh oh...

) defined in part by the fact that it takes a certain technical skill to make it! Likewise (not to make a direct analogy) Abstract Expressionism takes a certain technical skill t o make... successfully. And... likewise, it takes a certain "ear/eye" to appreciate these artforms. This is one way where I think notions of "elitism" come in.... Either one "gets it" or one doesn't... Either one is stimulated to tap his toes to a 9/8 rhythm or one is still trying to figure it out... And those that don't are not likely to feel comfortable around those that do! Sadly, this divides, rather than unites...
I think the art genre that actually affects society/culture at all is a damn lucky genre! 8) It usually relies on the intersection (collision?) of several circumstances that <I>enable</I> the genre to make such waves. But, it usually also relies on being absolutely new and original. Part of the success of jazz' is that it's been able to keep itself loosely defined; and it's been able to re-define itself along the way, absorbing influences at every step, and including a lot of cross-genre artists.... Is Allan Holdsworth prog or jazz?? How many jazz artists can remain "jazz" while crossing over to "prog". More, I think, than vice versa.... For example, how/why does Eberhard Weber end up in the "jazz" stacks???
I dunno... Maybe I'm wrong on that point... but it seems prog has, to some extent, had to resist absorbing too many influences for fear of losing its own identity.
When prog arrived, it was new and original, but I wonder (aloud) if it simply, by its nature (i.e. needing an appreciation of "chops"), wasn't "gotten" by enough people to make a bigger wave than it did...
One thing is for certain, it has clearly had a LONG-LASTING effect, or we wouldn't be listening to all these new artists on this fabulous station, having such (hopefully this is a bit) stimulating discussions some 35-40 years later!