My guess is that collecting is subconsciously about establishing order and control in some tiny portion of the universe. It's creating stasis in a choatic world. "I have this thing which has almost ceased to exist in the world, and it's like new, time hasn't touched it, and I can hold onto it forever (well, as long as I live)." Of course, it's irrational and a form of magical thinking, but what the hell? If it gives you joy, what's the harm, other than spending more than you can afford.
I often say I'm not really a collector, as I'm mainly after certain rare and significant texts, not first editions, but I bend that rule for some titles. Others by the same favorite author, I could care less what edition I read them in. It's quirky and tied in with personal history. For example, my favorite edition of ON THE ROAD isn't the hardcover first, which does nothing for me, but the paperback with the hippies on the cover (actually, there are two different hippie covers...I mean the brightly colored cartoonish one...the other, which is rarer, has a photo of hippies). Because that's the edition I read in college, and it'll always be my own personal first edition of that book. So I have to have it, while I feel no need for the hardcover in dj, and couldn't afford it anyway. Condition has never been too important to me, as long as it's all there and in one piece. I'm kind of a flaky semi-collector.