Here's a weird theory I came up with the other day, but haven't really been able to put into words yet (and I'm not sure if I did it justice here or not, but here goes).
I believe that in the near future, there will be an Atari 2600 "collecting crash."
Several years ago, I remember a lot of collectors talking about owning Pong machines. If you check the lists of many collectors, especially the younger ones, you'll find that most of them don't have them anymore. My guess is this is because most of these younger collectors never HAD a Pong machine, and have no desire to own one now either.
Collecting is rooted in nostalgia. Why else would we spend massive amounts of time and money trying to recreate "the old days"? Sure, there are some collectors out there who buy anything and everything they can find relating to videogames, but the majority of collectors buy vintage videogames because they used to have one.
Just for argument's sake, let's say people's "nostalgic memories" start when they are five years old. In 1986, the NES was released. That would mean that, most likely, kids who were born around 1981 or so (22 years old now) would have the NES as their first gaming memories. (Give or take -- this assumes all sorts of things, like at what age people would remember videogames, and that people bought an NES at launch -- bear with me, focus on the idea, not the exact numbers.)
My theory is, that the people that are getting into collecting now will remember the NES as their first system, not the Atari 2600 (like some of us) or even Pong (like a few of us old fogeys). My neices (ages 13 and 14) just decided they don't care about the Playstation anymore, and miss all their old SNES games. They know what a NES is but never had one, and the one or two times I showed them my Atari 2600 games they couldn't have cared less. As the new generation of collectors begin down the same road many of us have travelled, they will feel the desire to recreate THEIR childhood, NOT ours. Super Mario Brothers is the Combat of a new generation.
So, where will that leave Atari 2600 collectors? I believe that it will drive the price up for hard to find titles, and it will lower the price even more for commons. Most of the hard to find titles will have been found by then. So if you're selling, you're not selling to a kid but to an adult -- most likely one with a job and deep pockets. Likewise, anyone who wants a 2600 Pac-Man or Defender cart by that point in time will probably have one. 70's stuff was cool, 80's stuff is cool now, and as time goes on everything that was old is new again for a while and then gets old again after that. I've seen .50 cent games at thrift stores get marked up to $3 now, and in a few years they'll be back down to .50 cents.
The desire to play "the original games" on "the original hardware" is slowly sinking. The average person on the street has no way to even connect an Atari 2600 to their existing television. And even if they could, what's the point? Their PS2 is already connected, and plays Atari 2600 games perfectly. So does their computer, their handhelds, and maybe even their toaster! One could argue that you might want to play the games on an original 2600 just for the authenticity of the joysticks, but this is a generation who grew up with NES pads in their hands. A black 8-way with an orange button would feel completely out of place to them!
We've never had a generational turnover in collecting, just because videogame collecting hasn't been around that long! As 2600 collectors finish their collections and newer, younger gamers begin the collection adventure, I think you'll see the popularity of the original Atari 2600 slide by the wayside.