In my old band we had a singer, a drummer, and 3 musicians who were all good at guitar and bass. While we all had our respective roles (I was lead guitarist, we had a bassist and a Rhythm Guitarist), the 3 of us would switch around bass duties quite often. I'm not a good keyboard player, so the other 2 guys would occasionally play keys, and sometimes I would cover the bass. Sometimes we'd just switch for the hell of it, because it was fun and challenging. However (not to toot my own horn) I was the best lead player of the 3 of us, so I didn't get to strap on the bass as much as I'd like.
Now I'm trying to really come into my own as a bass player, not just a guitar player who plays bass. I've been taking lessons, because I really want to play bass like a bass player, not like a guitarist. I'm hoping to be able to market myself as a bass player OR guitar player, when the time is right for me to find another band. Right now it's too hard with having 2 young kids , a wife, a busy job and a whole bunch of other adult ******** to deal with. I consider myself equally a guitar and bass player now. I love it!