Whether you treat them as an investment or not. The games themselves are an ASSET. It is possible to buy a classic game on eBay, enjoy the game and then resell it at nearly the same price. Even if you resell it for a slight loss the $$/enjoyment ratio can be an outstanding deal because you don't get to keep that kind of equity when buying current gen systems and games!
I'm sure quite a few members on this forum could liquidated their entire collection, and while not make a huge profit, still have enough for a down payment on a house in most parts of the USA (certainly not Washington DC though).