well it may not apply past the beginner stages, but having more than one bass (that are different) to play on and get familiar with in the beginning stages, one learns about scale and neck geometry and maybe a few things about pickups and 'tone' and maybe matching strings to what a bass 'wants'. I don't think this would come in a few minutes in a music store. I bought a bass after a few minutes in a music store because the neck felt so 'natural', but after a few months at home I got tired of the constant wrestling with the body and neck dive and the hiss that I hear in the quiet of my house that I didn't hear at all in the store. And all in all that's a much better bass in most aspects than what I started with. Playing on one and then the other, the good and bad on both come to notice. Now I don't think any of that explains collectors with more than say 5, but I could see 4 pretty easily and a year ago I couldn't see what anyone would get from more than one.