For me too its XC Pro stuff when suntour went down the pan. What's more annoying was I was running all xc inplace of xt at the time (it's just better imo). Kept seeing it cheap, but thought " well its obsolete, something better will come along" . Well, no it didn't.
My personal "stupid selling award" goes to the 6 ma40 rims I had, when they stopped making them. I got them from a rep for a few quid a pair. My original set just went on, and on, and on, even radial laced. So i sold them years ago for not much more than I got them for....well you know, you live and learn.
But hey, it's important to concentrate on the good decisions we made, not beat yourself up about the bad.....also, if you kept everything you owned 30 years ago " just incase in became valuable " you would have no trade in value...so never would have moved on and be requiring a second house to keep it all in. 99% of it would still be old toot to boot!