I should also say that I like the idea of collecting different versions of games, including various demos, because older versions sometimes tend to fade into oblivion as they are viewed as "obsolete" compared to the newer versions, which isn't always the case. Earlier releases and demos often contain content that later got cut, and in any case, they provide a valuable insight into how a game evolved over time.
BTW, I think it would also be a nice idea to collect official pre-release preview images of some games, e.g. Apogee included preview "slideshows" of their upcoming games on CD releases, along with other goodies.
