A good solo whether on a piccolo, a bass, or a zither is a good solo. And a good soloist on any instrument can connect with an audience, and bring a crowd to its feet. This usually means thinking a bit out out side of the (bass) box, thinking as a total musician, as opposed to just a back up bass role, and dumbing oneself down. I agree many bassists have a hard time with solos, because that bassist must actually take the time to learn to construct a solo, learn what makes a good solo, know the entire fingerboard and play to the room (which may mean up above the dreaded 2nd octave part). A solo is also not just a bunch of rumbly fast notes. And I'd much rather hear a good bass solo, than some guitarist who only know how to Wank.