For me personally, I'm just keeping the machines that I have either A) Because they are dear to me for one reason or another, or B) I have a project in mind which requires this model of machine some day, or C) It's one of the machines I thought was coolest, which may just be a variation on A, or D) Who knows why I bought it, but I haven't had a chance to get rid of it yet.All these wonderful computers in storage though - are you keeping your older Macs as backups to working ones, or with the hope that in twenty years time they will indeed be your retirement next egg?
Oh, and E) I don't want it any more, but it needs some repair I haven't gotten around to yet.
I only recently finished cataloging all my Mac stuff and storing most of it in the attic (wish I had a basement). Now that I have an accurate list of what I have, one of these days I'll go through it and decide what I really want to keep, and the rest of it can go.