not as glamorous as the cars above but nevertheless a very serious factory aeromod was that of the opel kadett e, standard vs GSI
where the standard car had a 0.32Cd wich was quite spectacular for a small hatch in the 80's
but the gsi lowered this to 0.30 with the addition of small hood vents a rear spoiler a different bumpers and moldings in front of the rear tires
it's remarkable that such subtle changes brought about such a great improvement