My Westone and Ric are such different animals when it comes to tone and output level that if I am using one I tend to stick to it for a while.
The Westone has hot humbuckers with a thick sound, while the Ric has single coils with a thinner sound. The Ric sounds great with overdrive and distortion and other effects, while the Westone sounds best clean. The Westone's output is so high that I have to treat it like an active bass and engage the -15dB switch on my amp to keep it from clipping.
As a result, one is not really a suitable backup for the other. My Squier Jaguar is a better backup for the Ric as its output level is lower and it also sounds good with overdrive.
This is kinda what I'm thinking I'll have to do with my basses. They have very different ranges (though the outputs only differ on a couple of them) and so I think it would be most practical to get used to achieving a good sound on one of them and stick to it until I get tired of it and want to switch it out for another.
But then this brings up the question of a suitable back up bass. From what I have experienced, having all of my basses be different from one another makes it difficult to use any of them as a back up for the main one I'm using.

... Maybe I'll have to just suck it up and get more than one of a given style of bass just to fix this dilemma. Grrrr...
