TBH, I'm not sure if it's a Twilight or just a "slow period"........
Classic Gaming is a recent thing that grew along side the whole "retro" fads that started kicking off in the late 80's/early 90's, and I don't think that has been long enough to see what the long term cycle of fashion will be for this stuff.
I've always seen a small parallel to the music/fashion industry and what is fashionable/popular at the time. In the early 2000's, we were having a 70's revival on the heels of an 80's revival.....after a 60's revival at the beginning of the 90's and a 50's one at the end of the late 80's. Around 2000-2004ish, I saw the Atari 2600 considered "classic" instead of "sell it off for $20 altogether in a grubby cardboard box at the Salvation Army" junk, and watched the NES get to that point too.
If I were to make some speculations....
- certain consoles will always be popular, the NES, SNES, and 2600 come to mind
- certain games will always be cheap (think Super Mario Bros., Combat, Pac-Man, Pitfall!, Dragon Warrior, Zelda...and the like)
- when the quantities get lower, the prices will go up, but they will have a ceiling based on demand. I don't expect like Frank and Mike on American Pickers to pay $250 for a NES in 20 years to resell at their antique store for $320
- Some consoles will fade away except to certain crowds - I doubt the majority of collectors will want an RCA Studio II or Worlds of Wonder Action Max in the future
- And the mainstream will continue to whine and complain that the graphics are bad, the sound is ear grating, and that they can't figure out how to use a controller with one button and a stick, and that should should buy the Nintendo WiiWii 5000 with 12560P XSHD Graphics and a miniature DNA cloned orchestra for sound.