I have a few..!
Quite interested in why people have multiples?
For me, it's generally I want them all to have a different personality and tone - I like to keep an instrument (or a couple) designated to a project/band/album, the "flavour" of the bass aiding in inspiring my playing and guiding me to the vibe/parts I want to create! I'll experiment with strings, even tunings, different scale lengths and pickup configs all to contribute variety of feel and push me to be creative internally rather than following my fingers to the most familiar territory..!
I have one good pal (who shall not be named but is on BC!! Dunno if he will read this thread...he's probably too busy GASsing in the Basses for Sale section...) who has a *rather good* selection...I feel his collection is more about searching for "the one", the ultimate sound/setup for him...his playing is wicked -utterly different league to me, chops for days- and so his tastes and preferences are dialled in, nothing stays around too long unless it is a serious contender to be in that top 5%...some instruments edge closer on sound, maybe others for setup, others for aesthetics or woodwork...
Of course, for both of us there are others in the mix for backup, fretless options, 4 string flavours (we are both mainly 5str people) or an acoustic etc...
Another bass player I get to work with quite often is seriously dedicated to her main bass. I *think* it's a '78 Precision - well loved, mostly original. She is strictly a 4 string player...and yes, I think there are a few other tasty basses at home (maybe a vintage Stingray, possibly a J and certainly a couple of other good P's). So for tours, of course there is a backup Precision - but if at all possible she will be playing the main bass! It's character/action is part of her sound and all of that drives the band very well! I mix FOH for one of her bands and gotta say her top secret signal chain of P bass > DI (on some gigs it will be via a wireless, on others via a TU2) works fantastically. Every bit as good as other players with several grand's worth of preamp/pedals etc.
So yeah - if like me you have a few, or many...what motivates you to have the collection? I'm genuinely interested!
Tom