I'll weigh in (unnecessarily).
You should be able to play in all keys.
It's not as difficult as some would have you think.
Transposition on bass, as many have said, is mostly a matter of changing hand positions - the intervals on bass are regular and have constant spacing, so fingerings don't change. Changing key may have an effect when you're up against a boundary - the highest frets of your bass, the nut, the highest string, or the lowest string. (Essentially, if you had a bass with infinite frets and infinite strings, you'd realize that there's actually just one big seven-string pattern that tessellates. The issues only come about when you're at the edge of a finite fretboard area.)
Musicians who play instruments without constant spacing (brass, woodwinds, piano) or instrumentalists who may rely more on "absolute" positioning than "relative" positioning (some players of fretless instruments, perhaps in specific disciplines) may find it more beneficial to practice something in all keys. Generally, this is more important when you're playing a lead line and less important for accompaniment (read: bass players) unless you are playing a polyphonic, multi-voiced instrument like piano. Because we as bassists generally play single-voice accompaniment lines that generally provide a harmonic foundation, I believe we have a lot more leeway in what we are allowed to do (and what we're allowed to get away with) without affecting the core of the song or making it unrecognizable. (Jazz, where learning all keys is important, is essentially built on this idea. Repertoire, on the other hand, is the opposite, but in that case, you'd be sight-reading. Even in popular music - rock, R&B, etc - where a song may have a specific bassline, it would likely still be recognizable without it.)
In short, I think it's more important to understand what you're playing, be able to transpose by ear, and understand the keys enough to play and improvise in all of them (either using theory, or simply by ear). Essentially, become a good musician. If you're able to do this, then transposing a line or playing in different keys doesn't require work and learning - it just happens, and as such is a non-issue.
If playing in all keys will help you to achieve this goal, then yes, you should do it.