I've just been considering this point. On my bass, the action is 'medium', and looking down the neck, it looks like the rod could do with a tweak. There is that niggling feeling that I should sort it out, as the neck could be straighter and the action could be lower. The thing is, I love the tone and love the playability, so have to keep telling myself 'if it ain't broke, don't fix it'. If I fiddled with it, I'd be afraid if it didn't work out, I'd never be able to get it back to that bass I know and love.