This has been a fun thread to read through - my take on this might be a little different than some.
I love playing fretless but have never been proficient enough at it to warrant keeping one around (read: I suck) and I despise the sound and feel of flatwound strings, so I don't need to accommodate those peculiarities. That said...
My stable of basses currently consists of five:
1986 Yamaha BB300 in candy apple red, first bass I ever owned, refretted twice, J-style pickup added, brass nut added, new tuners, and properly shielded. Beat all to hell. I will never part with this bass for nostalgic reasons, but I never play it these days.
Ibanez SRX300 in electric blue, twin humbuckers, active, skinny little fast neck, acquired on a trade, practically pristine. Never play it, sits in a hard case under the bed beside the Yamaha.
Washburn Bantam B106 six-string in basic black, tuned E-A-D-G-C-F. I adore this bass for playing around with chording and for writing, and will likely do a good deal of recording with it this winter, but most of the time it sits in the hard case.
2010 Warwick Corvette Pro, pristine and recently acquired, incredible sound, haven't bonded with it so far. Still tweaking the setup - it's just not quite there yet. I have been gigging it a lot of late trying to form an attachment to it, and am thinking that the slightly higher, stiffer action might be better for live performance anyway.
2007 Ibanez SR506, purchased used online about five years back, my absolute go-to bass for anything and everything. Plays better than any other bass I have ever picked up. Action is just ridiculously low with *zero* buzz anywhere on the neck, flawless for tapping, slap, or fingerstyle. I must have just lucked out, because this bass sets the gold standard for perfection IMO. Even with the strings pretty dead it sounds and plays better than 99% of the other basses I have ever picked up.
If I had to choose, I could run with only my SR506 and never look back. Yeah, I would be a little peeved to lose the Yamaha or the Warwick (especially since I am still tweaking it and might yet get it perfect), but realistically, the Ibby would handle *any* gig I would ever be asked to do. Assuming nothing significant changes it will like as not be my favorite go-to until I die, which might happen sooner rather than later if I don't stop hauling basses into the house. LOL!
OP, I get where you are coming from - when you spend a *lot* of time on one instrument, everything else feels a little 'off' by comparison. Not necessarily 'bad', but definitely not what you're used to. When I first received the Warwick last week I changed the strings to my preferred set and did a complete set up, but when I tried to play it I was amazed by how different it felt from my SR506 - the same exact strings felt *way* more tense by comparison. My first reaction was, "OMG - I just paid *how* much $$$ for this thing?", followed quickly by, "Where's my Ibanez?" LOL! I powered through it and am enjoying the Corvette now, but it was super-weird to begin with. I had been playing the Ibanez for the past five years almost exclusively and ANY other bass felt really strange.
After buying the Warwick I felt a little bad having so many basses in such a small place, and was planning to sell the SRX300 and Washburn (after restringing to a more normal B-C tuning), but the LSW intervened. She pointed out that where we used to live, buying and selling instruments was easy - I had lived there for over 40 years, knew everyone in the music community, and instruments were comparatively easy to come by. Where we live now, the music community is smaller and cliquey, and there are no real local music stores, so she admonished me that I had better just leave well enough alone, as I would be hard-pressed to replace anything that I sold at twice the price.
Gotta love that woman.
So OP - don't feel bad that one particular bass has the lion's share of your affection - I think it happens to most of us at one time or another. That said, it's still nice to have a few others around for a little perspective or inspiration occasionally, even if you always run back to your old favorite.