Basses I've had, and some I've sold or traded...
I was pretty poor, back in the day. Couldn't hardly afford more than one bass at a time, if that.
My first bass was a Hagstrom. Hagstrom II, I think. I broke it in a fit of temper. The problem was that it wasn't really my bass. I'd borrowed it from a friend of my brother's. Had to buy it from him, and I still had no bass.
I'm not sure which came next. I had a Fender Jazz bass, which I didn't much care for. The neck was narrow, which I liked, but thick, which I didn't. A previous owner had put in a Gibson mudbucker. I think it was between the neck and the Jazz neck pickup. I didn't like that at all. Around that time, I also had a Hagstrom 8-string. Maybe I traded the Fender for the Hag, but I'm not sure. Anyway, I haven't ever missed the Fender, but I did miss the Hag. At any rate, whichever I had, I then traded for a Mapleglo Rickenbacker 4001. I liked that bass a lot.
Wanting something more stylish, I bought a Ric 4000, and had it modified. White, with black pickguard and truss rod cover. I still have that one. Not long after, I traded the Mapleglo 4001 for another Hagstrom 8, which I also still have. The white 4000 was my main bass until I joined the Navy.
While I was in the Navy, I didn't play much. Something went wrong with the wiring of the 4000, so I ought a cheap P-bass knockoff. I think the brand was Cameo. Never liked it much, but it was something to play. Like every P-bass I've played, I found the neck too thick for my taste.
The score: I regretted breaking the Hagstrom II, selling the Hagstrom 8, and selling the Mapleglo 4001. Haven't ever particularly regretted selling the Jazz, but I wouldn't mind having it back again.
After I got out of the Navy, I had more time and more money. Eventually, I got into a band, playing guitar and keyboards. I fixed the 4000. A friend asked me if I knew where she could find a cheap bass for her daughter. I told her I'd refinish the Cameo, any color she wanted. I got the old finish off (not easy, as the body had been dipped in something - epoxy, I think - before it had been painted). By that time, the daughter had lost interest, so I finished it in transparent black instead of the pink the daughter had wanted. Stepfather loved it, so they bought it anyway. I don't particularly miss that one, either, but I liked the way it looked when I was done.
And that was the last bass I parted with. Since then, I've accumulated several more. Some might say, too many. But I'm playing bass in three different bands, and five or six of them get regular use.
My thought on selling your first bass? Unless you really don't like it, or absolutely have to, I wouldn't. I ended up replacing the red Hagstrom 8 (I now have two) and the Mapleglo 4001. If I ever come across a Hagstrom II, I might consider buying it. They have a shorter scale and very fast necks. Would be ideal if a person wanted a bass strung ADGC, though I don't particularly think I want that. Still, your first bass is like your first love. You never forget it, even if you're better off with what you have now. But, with basses, you can have both!