i (usually) never do... there's often "good stuff" hidden away in various releases that MS deems too good for the average joe, so it gets eliminated in future versions.
I forget exactly what it was, but 2 years ago I had to hunt down a copy of windows 98 (1st edition) because they took something out in win98se.
I regret throwing away my windows 3.1 software a few years ago. And I also regret throwing away an old 286. My favorite game of all time (688 attack sub) was made in the olden days, and todays lowest-end refurb is too fast to run it

(although when I have time, I'll try to get it running acceptably in dosbox)
I've also been paranoid about the revolution in video(and audio) encryption/copy-protection/DRM, so I've been hoarding some usefull softwares. I suspect there will always be "a way to get it" -- but I've witnessed too many things vanish.
Anyway, if you think I'm crazy, you should donate things that work. Charities can write up flyers in Office-97 as well as anyone else can in whatever the current release is.