Tube preamps, the really good ones, can be wonderful things. specially so on guitar, but also can be on bass.
Tube power amps, for the power you need for bass guitar, are NEARLY always (yes I am aware of a couple of exceptions) very heavy, expensive, heavy, hot, heavy, weigh a lot, picky about the cab impedance, heavy, and are not light.
At least in my 50s now that is the biggest memory I have of the tube amps I used to play through as a bassist. And I played through ampegs off and on for years, ampeg all tube heads, as well as music man tube power amps, for bass.
the only tube amp I still own is a Genz Benz El Diablo 112 combo... the single greatest guitar amp I've ever owned in my life. But it just lives in my music studio.... way too heavy for me to move around. But WHAT an amp. It is the only non-presettable guitar amp I've owned over the years that I still own, other than cheapos lying around the house for convenience. All other guitar amps (and non amps, like modelers) I own can be configured for total recall of all parameters with footswitch etc... but if I am searching for the ideal tone on guitar, that Genz Benz amp is far more versatile than any other tube amp I've worked with, while having exceptional tones all over the map.
Still, that being said, you may well love the features you are looking for in a tube preamp, as has been discussed already, without a very heavy and hot tube power amp stage.... a good bass tube preamp, like you said, that is sexy. I even agree that they can be sexy looking, although that often isn't the priority for bass amp designs, from my experience.... looking "tube-y".