For two day meetings I always used to completely strip and redo the diffs and shock. Now I just do the shocks (but only if I have a run before the final as if the ride height drops in the main it is not good). I stopped doing the diffs when I rebuilt them for a main the next day, and then it destroyed itself, so I must have built it wrong. So basically I stop the chance of me redoing it wrong, so just more the 'if it aint broke' approach.
In between runs it is generally just a check, and got to clean wheels, wing and shell! 'Presentation is part of performance' :P As it is as much about your attitude towards your car as some small setup changes
Scott