[aerohead]

After study of the official SAE practice for coastdown testing,I have little confidence that any of us could meet the stringent criteria to pull it off,such that you could measure subtle changes as would result from lowering the car.
This sort of thing would be relegated to a wind tunnel where every conceivable variable could be tracked and recorded for later data reduction.
In the article about the recent land speed record for the VW Jetta hybrid,they noted that the dual mirror delete,wiper delete,narrower tires,and lowering, were not enough to affect a Cd change,but did lower frontal area so as to definitely effect CdA,as already mentioned.