Yep. I've sold some nice instruments. And amps - I sold the blackface Bassman from my studio when I closed the business, along with my JCM800 and a couple of others. But I regretted selling the Bassman literally within minutes of it going out the door. It was years before I got another.
The guitar I miss most actually wasn't one I sold. It was a '56 Black Beauty reissue that I bought new in '74. Had the staple neck pickup, incredible sounding guitar. Super heavy but at the time I was young and had no problem with that. It was stolen a few years later by a junkie we'd allowed to stay over at our house, who likely sold it for next to nothing. It'd be reasonably valuable today.
On the bright side, at least I'm not kicking myself for selling it...