The great player sounding great on a lesser instrument posts have no meaning at all. It is short-sighted and has no place in a discussion where a person wants to upgrade to a nicer instrument.
Pretty much any pro can pull what need out of most basses for a couple of sets.
Beside how an instrument plays, the biggest question is: how much work you can get done on it in the practice room?
Ray Brown can sound fine on a lesser bass. He became the Ray Brown we know practicing on a good bass.
Just because the tone is in a bass, does not mean anything when trying an instrument to own and to do your work on it. If you want to get anywhere with the instrument, the bulk of that work will be in the practice room, playing things that are not all that fun. A nice, inspiring bass you don't have to fight for tone and projection is key.
Listening through a set up not optimal for you is a bit harder, but you should factor such things in.
A few weeks ago, Luke Stewart was in town and I lent him my bass for a show. I gave a hard no on lending it for school program as things get damaged at schools.
My student brought over a nice, well set up Kaye to lend for the school gig. It had a nice, strong warm tone. I could get a lot of my sound out of it both arco and pizz. Compared to either of our basses (he plays a higher end fully carved Shen that sounds and plays great) it was exhausting to play.
So, really think of what two or three hours of practice will be like on the instrument you choose. Not just how a couple notes pop out and whether it will be adequate on a gig.
This is kind of what I was trying to get at but never brought it back around. A nice bass that is finicky and has more wolf tones or some other trade off for its sound can be a real pain in the arse after even just a warm-up and not be worth the money or pedigree. It can be easier to sound way better on a more agreeable bass which makes the whole cost less of a factor in trying to find an upgrade. It's all about finding a /good/ bass.