It's kind of a tough call. In my case I keep a library of Blu-Ray and DVD disks. I've ripped them to network storage so I don't actually need them, but I did spend an amount of money collecting them. So at this point I just keep them for posterity.

In general I have a rule about not keeping stuff I don't use, but there's always exceptions. There's been a few things I've wished I had not parted with, but if you never get rid of anything you're just hoarding. I'm more of an anti-hoarder and it's cost me before. On the other hand there's too much "material stuff" in life. Best to keep it minimal.