If you're a decent guitar player, you'll have a pretty good sense of where to "find the notes" on a bass. Playing bass also gives you a generally better sense of where the scales and intervals are on a guitar, and it makes you more conscious of the bass notes in your guitar chords. It's worth it to play both, I think. Plus, bass is generally less complicated. Less pedals and knobs and cords (and chords) and buttons...simpler, and fun to play.