I don’t regret selling anything specifically but rather, I regret selling everything. Lemme Splain...
I was a radical gear whore for many years. I bought and sold stuff far too frequently in pursuit of the elusive “perfect gear.” I bought high end Basses and only kept them a couple months, only to sell for less than what I paid. Same for cabinets, amps, pedals, rack pieces, etc. In the two years after my divorce alone, I literally spent around $50k on gear. I wasn’t even gigging and I bought 6x10, 4x10, 1x15, 2x15, etc. cabs, tube amps, ss amps, combo amps, multiple high end Basses (Sadowsky, I believe I had 5-6 warwicks, several spectors, many others.) Had I realized that there is no perfect (like I understand now) I could have been happy with what I had and saved myself a lot of cash.
These days, I’m much more content with what I have. I wish I would have figured that out years ago.