My thoughts on posts like these are the same as a few people have mentioned. Essentially, don't let the door hit your rear on the way out.
In my years on this board, which are (within days) going to number a total of seven, I've seen dozens, bakers dozens, maybe even more than a hundred people come and go. A lot of them come on, post a bit, then fade out, and some of them come on the board, cause lots of trouble, allow their accounts to get hacked dozens of times, get banned and then evade those bans, and then finally post a big dramatic "well, I'm done here!" message.
I'll let you decide what situation this is.
In terms of hoarding, what I've found is that it's a matter of how much you can physically store, and the other part of oit is what would you be physically capable and willing to take with you in the situation that you needed to, say, move across the country. (Latitudinally or longitudinally.)
The size of my collection of usable computers that's with me has fluxuated over the past few years, ranging from "just one laptop and one external drive, plus a binder of CDs" to "between fifteen and twenty desktops and laptops." Just in my dorm room, and that has fluxuated with my physical capability to manipulate them within my alloted space, and with my physical capability to move them all when I need to.
Of course, those issues aren't big for everybody, I know many of us are pretty much where we want to be physically and everything, so having a basement chock full of machines is really not a problem.
So in terms of "hoarding" I think there are no universal hard and fast rules. My level of concern is about 8 machines, most of which need to be tiny or laptops, so before I allow myself to get another (I'm at 7 now) I need to re-evaluate which of the machines I have I ever use, and which I can get rid of, either by putting them back at my dad's house, or recycling/selling/giving.