I still have all of my 2nd edition stuff, and a fair amount of 1st edition stuff. (When do the charts in the back of the 1st edition Dungeon Master's Guide stop being useful? Not yet, for me, anyway!)
My 3rd edition stuff will likewise remain useful for ideas, inspirations, etc. even if I never played 3rd edition again (which seems pretty unlikely, since my campaign is set there and I'm not prepared to convert everything to 4th edition, any more than I'm ready to convert it to GURPS).