I can imagine!
Personally, I don't regret selling basses. None of them are collectors items (for now
) and they were just too much to keep. Some sales were tough decisions (my Rickenbacker 4003, I really needed the money) but looking back, I don't miss any of them.
In two occasions, I actually bought back basses (well, identical ones) that I felt I missed.
The first was a MIJ Condor Jazz Bass copy in proper 70s trim with blocks and bindings which was my very first bass. A cheap Japanese bass from the late 70s or early 80s that I really liked but didn't touch anymore when I got my second bass. I felt I should have kept it because it was my first bass and I thought it was actually a pretty good instrument. Was I wrong! When I got an identical one, it absolutely SUCKED! I'll never know if the first one I owned was really a much better instrument, or if it was just me not being able to properly judge an instrument back then
The other one was my Yamaha TRB5II I felt I should have kept because it was my first proper bass 8 years ago, but when I bought another one last summer because of these sentiments, I found myself playing only one gig with it and retiring it to gather dust at home again. It's a great bass, but I have so many great basses that I just didn't play it so I sold it again last spring.
My regrets mostly concern basses I didn't
buy and wish I had
I really missed some once-in-a-lifetime opportunities, for various reasons...