Bass guitars are an essential instrument for keeping rhythm and simple melody. While I myself have only played a bass guitar on occasion, I appreciate the bass guitarists that I have jammed with.
I think it is a good idea for a serious guitarist to at least play bass lines on the guitar. This helps the player to gain valuable timing skills. When I am trying to learn a song from ear, I usually try to identify the bass guitar. This helps to then find the correct key, beat, and melody. From there, I can then fill in with the proper chords and scales.
What I have noticed throughout the years, is that the bass guitarist is typically the unsung hero of the group. The picture of the bass player with the dark sunglasses, standing towards the back of the stage, calmly plucking his strings is the epitome of laid-back coolness. Of course, there are some obvious exceptions to that stereotype, but by and large, most bass guitarists seem to be the quiet, logical members of the band, if not a bit eccentric.
There have been times when I have been tempted to make the jump and play bass guitar in a band. But lo, I do not feel as if my personality type can fit into that of a bass guitarist. For now, I'll have to be satisfied with the click, thwack, beep, bop of other bass guitarists.