To show that I practice what I preach: my electric stunter which would get possible 5 appearance points! If the judges are having a good day, my score will more than make up for lack of A.P. Why worry?
You aren't going to give up 2-4 points on Top 20 or Top 5 day and "make it up by flying" against Paul/David/Doug/Derek, or at least it will be prohibitively difficult. In Advanced or Expert at a local contest, then, sure, most of the time you can give up appearance entirely and still have a chance. That's why the BOM debate is as it is, it's about the NATs, and nothing else.
My analysis from the time I have been doing it is that appearance and flying are about 50/50 in the results, depending on the points range. In the late 90's the tendency to select judges for absolute score biased it towards appearance a bit, and with the automatic method increased the score range and biased away from appearance a bit, but over time the value has tended to be about equal.
It actually makes a pretty big difference on Top 20 day, too. I missed on appearance points in both 2001 and 2002, but there were plenty of flying errors, too. My solution - build an 18 point airplane instead of a 14 point airplane. That's part of the event, it should be part of the event.
Brett