I've owned a lot of crap so I don't have any big regrets but the one I miss the most is my epiphone excellente. It was an absolutely stunning guitar and about as hard to find as they come but its tone was far too dark for me. I was impatient and sold it for much less than I should have.
Probably my biggest regret was selling this Rickenbacker 620, I bought it new for around 1100.00 dollars sold it for 850.00, you can't touch these for under about $1400.00 dollars theses days
I am lucky enough to have not had to get rid of a guitar that I have missed. I feel for the guys that had to get rid of a special one out of necessity (bills, mortgage, etc) but for every one of those there are 10 with grass is greener syndrome that end up with a turd. I have no sympathy for the latter.
Early eighties BC Rich Mockingbird Supreme custom made with H-S-H passive with 3-3 way toggles to control the pickups plus a phase switch for about 50 combinations.
Real warm sounding Koa with a Duncan '59, tapped single coil , and JB or Stag Mag in bridge, should not have sold that one.
About 6 years ago I found myself in a very bad financial spot in life ..I had to sell my '82 Charvel strat head and the one and only Splawn modded Marshall with 3 gears . I'll take that shit to my grave ...