Validation of your argument is based on the design pull-out of the plastic push pins? Go pull one out of your Mustang, count how many there are on each side and perhaps you'll rethink that a bit.
It's not validation, it's correlation. I said i don't know what the impact would be. OK, just checked my mustang. No plastic push pins. 10/32 screws and rivits from the aluminum skirt to the plastic rocker, and then to the steel jacking rail welded to the pinch/rocker.
Skin friction drag? Really? Differences that matter for an airplane, but matter very little for cars that average around 70-80 mph around the track. I don't think there's a practical way to quantify those differences...in actual testing *or* CFD.
Most definitely. When i was an MX-5 cup engineer, we raced with IMSA as a support series. I chatted with the head Porsche GTLM engineer for awhile and he told me that they wax their cars before qualifying for this very reason. As you know, drag increases with the square of speed, so the average speed around the track isn't the important bit for factoring skin friction drag.