Store them if you can, but tossing them is a bad idea if irreplaceable.
2. The lifespan issue is documented here: http://www.clir.org/PUBS/reports/pub121/contents.html A PDF or full download is available if you need it.
I have been buying Maxell, Imation and Memorex DVD+R's and was wondering about the shelf life. How long can I expect them to last. I have been transfering my video tape collection onto DVD'S and am about to get rid of some of the tapes since I have about 500 and they are taking too much room up. I would hate to get rid of the tapes and then later on have a DVD become unplayable.