The only advantage to unlined is aesthetics. If the lines bug you, get an unlined bass. My first bass was an unlined fretless. I have no issue with playing unlined. I'll only buy lined now though. I frequently find myself in spots where I have inadequate monitoring, and those lines have saved my butt more times than I can count. As for the lines not being 100% accurate, that's completely true. They are pretty close however and it's easy to learn whether you should play on top of or slightly behind the line depending on where you are on the neck.
Playing on the lines in a poorly monitored area isn't gonna be much better than playing unlined in a poorly monitored gig. Ears win on a fretless, never eyes.