Re: Should I learn the bass?
Playing the bass is great fun, that's for sure!
I'm a guitarist primarily (with a focus on drumming for the last 2.5 years) but kept playing a little bass just for fun/in case and to arrange bass parts for my orig. music (most of which is written but not recorded yet). I have 2 basses - see pic - but didn't ever use them live (started performing live under a year ago, at age 39, haha) until yesterday. That was a rather small band - female singer, el. piano player, me on the bass, and a conga and trumpet player on a few songs. Besides the pure fun of just playing it will also raise your awareness of how songs work in their entirety and what/how everybody is contributing to the final result. You also get more into understanding harmonic structures - I guess this has already been mentioned in the thread, haven't read it completely.
Those basses are a 6-string by Tune (Asian manufacturer) and a Magnus Krempel (German luthier) 5-string fretless, I bought both of them used. I finished reworking that fretless (stripped the orig. finish and put some tung oil on it) just in time for yesterday's gig - used it on a couple songs only as my intonation on the fretless isn't perfect (yet).