Video game collecting is generally regarded as a poor investment if you're looking to make cash off of it. There are plenty of great articles on the subject, such as :
http://www.racketboy.com/...nt-invest-in-vintage.htmlA big factor in keeping game prices down is the re-publishing of some of the rarer games. Game Quest Direct has been doing a fantastic job reprinting games that are hitting crazy prices, and are branching into the older systems soon, like Sega Saturn.
The market for rare games is also extremely small. If you ever look at an Atari 2600 rarity guide, even level 8 rarity games can often be had for less than the original cost of the game in the '80s, factoring in inflation.