Don Firth has it right IMO - that's just what I try to do myself (not that I'm trying to claim I'm anywhere hear as good as JB). Being able to make variations in the accompaniment in the way Don describes not only makes it more interesting for the audience, but for me too. It's better to have a lot of techniques at your disposal that you can use almost unconsciously (which takes a lot of practice) than to just work out a rigorous note-by-note arrangement which you reproduce every time. The artists I enjoy the most live, are those that never do a song exactly the same way twice.