I really don't think bass is suited as a lead instrument. It's expressive, sure, but as expressive as a voice, guitar, violin, trumpet, piano? I don't think it's quite up there. I love bass because of the way it glues everything else together, and there certainly ways to be innovative and melodic while doing this. In terms of timbre and range though, for me using bass in a lead context is putting a square peg in a round hole.