I tend to go with nostalgia as a good enough reason. I've been working on collecting every single computer/console item I've ever used personally in my lifetime that was not work related. No real reason other than I enjoy the collecting and the nostalgia of playing the same games I did as a kid on the same hardware. Waste of money? Perhaps. But like many old items, they tend to appreciate in value so long as the remain working and they make my man cave look retro cool. I just bought a lovely Apple IIgs to complete my Apple needs, and have but a single item left in order to call my collection done. Laughably, it is easy to buy but I've just not found the perfect unit for my needs... a C64. Tons available though, so I expect I'll find one that grabs me one of these days.
Not saying I won't collect a few other items as well, as an Amiga would be a nice addition but I never had one or used one. Same goes for a Tandy 1000. But you can't have everything, and I don't have enough room to setup and display everything I have now. Still, I enjoy the retro hardware too much to not consider more collecting. Or "preserving" as I like to think of it.