I'd say 'it depends'. I'm a jazz guy, and I want to get as much paid work (studio, GB dates, etc) as humanly possible, and I also do a fair amount of theater work, writing out horn charts, etc. I'm not the best sight-reader around, but I can muddle my way through it fairly quickly. For my purposes, sight-reading standard notation is indispensable. My goal with that particular skill is to be able to read it just like I read English, and be able to play a chart 'cold' around 180bpm. Right now, I'm able to do 'simple' charts (walking lines, etc) around 40-60bpm, with an accuracy rate of around 80-90% (remember, this is reading a chart completely 'cold', never even having heard the tune before). It all depends on what you hope to accomplish musically.
Also, being able to transcribe stuff off of records, be it basslines, horn/guitar solos, whatever, gives me a completely different take on approaching music and my understanding of different styles and whatnot. It's awful hard to transcribe from one instrument to another in 'tab'. I'd say the benefits of being able to describe position via tab are far outweighed by the portability and rhythmic specificity of standard notation (again, just IMHO and for my own needs).
If you really want to give reading the ol' college try, I'd say get the book 'Essential Sightreading Studies for Electric Bass' by David Molto, and a metronome. It starts out with the absolute basics, and slowly builds up to more complicated passages. It's a short book, I'd recommend doing just a single page from that book each day. That way it's a relatively low time commitment, but it's a REGULAR time commitment (which is key for learning a new skill like sight-reading: recency, frequency, and repetition) In less than 10 minutes a day for a month, I think you'll see a huge improvement in your sight-reading capabilities.
Just my $0.02, hope this helps!
--Lee
EDIT: quick correction, guys. My apologies, the book I was thinking of was "Essential Sightreading Studies for Electric Bass", by David Molto. Many thanks to kesslari for bringing that to my attention!