I find it most convenient to use a multiple-bass stand (in my case, a 7-instrument box that folds up to look like a guitar case) because I play them all frequently and switch from one to another a couple times a session.
The temperature/humidity thang is problematic. Yeah, it makes a difference. No, keeping them in the case doesn't protect them from either very much. Yeah, one of my basses has a neck that swings back and forth like a garden gate, takes neck adjustment twice a week and bridge tweaks daily. No, the other basses have necks that move seldom (and very slightly) to never. Keeping them all in the cases makes no difference here - the active neck moves, the others do not.
I also have a couple instruments (one bass, one guitar) that I might pull out once a year (actually, I've played that guitar once in 25 years!). Makes sense to leave those in the cases where they are safe from dust and accidents.