I have a bit of a theory as to how Wii games will incline in their rarity and value in the next 20 years, when it becomes in a sense "old school" like the NES and Atari VCS is today. It's apparent that there is a multitude of shovelware software for the system- games like NinjaBread Man, CID The Dummy and Mini Desktop Racing. Nowadays, online resources allows us to evaluate just what you're purchasing- wheras back then you had to go on impulse and hope to God your fifty dollars wasn't thrown out the window (magazines like Nintendo Power praised ANYTHING coming to NES). These obviously means that not many people are going to invest on these games unless they're oblivious parents looking for cute games for their five year old children. As with older games, it's very possible that a game shop overloaded with the titles will send them back to their respective publisher- which would lead to the destruction of these games. Take Spyborgs (Wii) for example. It has only sold about 500 copies, and if stores do not see an increase in sales they will not buy more copies and/or send them back to the publisher to destroy. If this happens, those owners of the 500 copies are going to find the game extremely rare years later- if the rest ever produced are destroyed, that is.
Look, I'm just a dumb 14 year old who knows nothing about marketing- but I think this could be a possibility for the future of game collecting.