A lot of people collect only games they like to play while many others like collecting whatever they can get their hands on. What do you think is more impressive when it comes to display? A large stack of almost 2000 games even though most of them suck, or a smaller collection of just a few hundred games that are actually fun or part of a series?
My collection consists of many loose cartridges and game discs that I bought dirt cheap when a game store was being liquidated, but I also have many good games in there. The thing is that I have the idea that I might like to pull out each game and at least give them one try. Personally I would like to hang on to these because I can imagine that if I ever did want to complete a system set it would be hard to get all these back again for under $2.50 a piece (when shipping for 1 game is usually no less than $3 anyway). It's probably worth more money to hang on to them.
At the same time, it's getting harder to store the collection and there are better games out there that I still don't have.