I (largely) sold up in the early 90s when I went back to college. I'd only been collecting about 10 years, but I had some OK stuff that I could never afford to buy back now
(L. Allen, Willie Tee, Terry Callier, Melvin Moore, Barbara Long, Bobby Hutton and so on). Never got more than £100 for any of them, and in some cases a lot less.
What irks me more, though, is that I also sold a couple of bulk loads of pressings, Grapevine singles and 80s releases, most of which I had bought from Soul Stop for 50p each, and I sold them for about the same money. While some of these records have gone on to be relatively sought after (Master Force is one that leaps to mind), others have just gotten ridiculously expensive in relation to their rarity. Since when is any UK Grapevine single worth the £50 - £100 that is now routinely being asked for Flame n' King, Lester Tipton, Betty Boo and others? Never mind, buying back the US originals, I can't even afford/bring myself to buy back the Grapevine singles I'd like to own again.
Conclusion - don't sell unless you have to, or you are completely sure that you never want to own records again.