A lot of people I chat with believe the market is a bubble and it's on its way to bursting. Atari used to be relatively expensive for a period of time, now it's relatively worthless. People think the same thing will happen with the NES.
I don't agree, but I do think a lot of people who are collecting for nostalgia's sake will likely give up at some point, or maybe they get married and have kids and have to change their priorities.
I know I am and have been pretty burnt out lately. I took a break back in March to chill and just enjoy what I have and focus on saving money to buy a house. We bought a house, now I'm able to get back into collecting, but I just don't feel it anymore. Trading with folks online is troublesome because the people I would trade with seem to only want mint condition stuff for display rather than games to play like they used to. Buying stuff on ebay/CL/facebook is just useless because people throw ridiculous prices out there expecting nothing less because it sold for $10k on ebay VGA graded 4 years ago, so my MINT game with no label, box, or manual is worth at least that. Yes, that happened, often actually, and yes, I am bitter about it.
In a different situation I would think that the bubble theory would work, but when the big thing right now is streaming let's plays and such, no title is safe. Some day, a guy is going to do a let's play of a game like Fear Effect and people are going to go banana's and drive that price from $20 to like $50. Shenmue for dreamcast used to be a $20-30 game, now it goes for like $40-50. All because of hype. If streamers, kickstarters, and word of mouth can keep hype going for the hobby people will always be buying something.
Now if MLG and Streaming becomes a fad and nobody cares about it anymore, sure, it'll die down. But as always, people love to live vicariously through others.