I think a proper setup is necessary, particularly for intonation and action, but not so sure if everybody should attempt it themselves. If you are not a "mechanical" person, leave it to someone else or have someone who is confident assist you. OR pay for it to be done. I've bought basses off guys who had been playing for years, but the intonation was quite off.
I am quite prone to living in the 12+ fret range, so having a good setup and dead-on intonation is not optional. Funny commment someone made about guitarists with terrible setups - I bought a friend a used guitar for his b-day and yes, I suspect the previous owner never played it because the bridge was setup with all the saddles straight across, which was nowhere near correct. My friend had never had an electric solid-body before, so he got a real treat, learning/watching how a proper setup is done - and the guitar now screams.