Depends if the question only applies to CE.
Gaming in general, I've been keeping complete copies of my games since my NES days. I always thought they looked neat on a shelf, even as a kid. I'm really glad I did. Only a few of our very first games no longer had boxes --- and it was expensive enough to hunt back complete copies on eBay! No way I would have done that for all of them! I guess I just always had this "collector" mindset. Now it just makes me happy. Games always bring back so many great memories. I like to sit down, look at all my games and then just pick one to play.
As for CEs, well, I mostly started picking those up because they tend to look amazing... and of course, I love the extra stuff! Especially figures/statues and the such. Looks great in a collection! I don't always pick the CE over the regular edition, though. Some just don't come with anything I really want and I'd rather put the extra money on hunting down other complete games (Earthbound, you're finally mine)! This is pretty much why I haven't been around here as much. I feel like I have nothing to share. ;;;;