That is the bittersweet reality of analogue cameras these days. Really easy to get involved in, but only because so many are losing interest. I know I'm lucky to have a camera that in the 80s would've been considered a semi-pro not-for-amateurs system. I think what I'll do is use the 645 like crazy (I already go out and shoot at least every other day), and I'll save a little money each week for splurging on cameras that interest me (c330, RB67). I won't keep more than three cameras at a time, especially since I go to college soon and having 5 medium format cameras would just be overkill.
My dad does that with guitars, and it's worked out pretty well for him. No clutter, but he's still able to try ones he's interested in, and maybe even make a little money selling them.