I've bought/sold many basses over the years, and I can honestly say I don't miss any of them. It's not that they were bad basses, I guess they just didn't fit me. Among those basses were a USA Lakland, 2 high end Zons, many Steinbergers, Warwicks, various Carvins, and a high end Spector. Most recently on the high end was my Music Man Bongo. I honestly would not buy a single one of them back unless it was an insane deal.
My current lineup is a Warwick Streamer Jazzman, a Spector NS-5H2W, and a Brubaker Brute. It's taken this long to figure out the neck shape and string spacing that I like.
There were some close calls though. I had a 1996 Warwick Fortress One that I never should have sold. Not that I 'miss' it really, there was just no reason to sell it, other than to buy something different. It was a better bass than most anything that came after it, and it took another Warwick to beat it.
Steinbergers. I've had probably 5 Steinbergers of all types and shapes. I'd like to have one of them back just to have a Steinberger. Overall the best one was an old pre-Gibson Q4. Felt great, sounded great, I think I paid $300 for it. Sold it for some stupid reason. I also liked my Gibson era Xq-25, it sounded phenomenal and the neck is perfect. Just wish it had wide string spacing.
Zons. I had two NICE 5 string Zons. One fretted, one fretless. Beautiful basses, loved everything about them except the string spacing and neck shapes.
I went nuts one time at a guitar show and bought a USA Lakland and a USA Spector NS-4. Couldn't get a good E string sound out of either one, so they didn't stay long.
I had 3 Carvins. Eventually sold them all. May have kept the Bunny Brunel if it were fretted.
Warwick Thumb. One of the best sounding basses ever, nice thin neck that just begged to be played, just couldn't jive with the body.
I sold my Bongo because I needed money and at the time it was the most easily replaceable bass I had. Just never went back to a Bongo after getting my Warwick.
Yeah I'm going to revise my previous statement..I want my Steinberger Q4 back!