I think Mike brings up a great point about learning vs timing vs quantity.
My studio and my studio "life" as such are divided into two distinct areas,
On the recording side I have a pretty hard and fast rule that If there is a piece of equipment that I have not used in six months or so, I usually sell it. It makes no sense to have a studio full of stuff that sits there and does nothing while we tend to gravitate toward certain pieces over and over.
Only once have I sold a piece I regretted, I spend much more time wondering..."Do I really need this and could that money be better used elsewhere?"
Anyway, I know that for many gear hounds and synth enthusiasts this is pure heresy...
Paul, I think you're right that many gear hounds and collectors are much better at acquiring new equipment than at selling it or getting rid of it. But I think your approach is sane and practical, and I'm trying to figure out how to get there myself. I made some efforts a year or two ago to get rid of maybe 10 pieces of gear that I wasn't using at all. I still have some redundant or (for me) obsolete gear that I think I'll try to sell soon. Maybe after the new year I'll make a little list and put it up here.
Lately, though, I'm moving the opposite direction, having purchased two pieces of gear in the last few months from people selling it here on the Forum!