I got rid of loads of my old boxed games when I moved out, ym Dad was all "you don't want to keep these do you?" At the time, I didn't really think I'd want them in the future.
I occasionally buy old boxed copies from eBay of games I used to have. Building a decent collection now.
Amongst all the boxes that went to the charity shop was a copy of Star Wars: Supremacy. Which I miss not 'cos it's worth anything (they crop up on eBay for a tenner every now and then) but because it was a great game I miss having.
Oh, and PC Dalek Attack. Which is now a basically unavailable Dr Who collectible...