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The lowest drag 4 wheelers have narrower rear tracks, anyway. The Cd *far* outweighs the frontal area, especially when the Cd is is as low as possible.
Ken is correct about the rolling resistance of the tires -- if the weight is the same, then it doesn't help to have 3 wheels instead of 4. I think there may be a small difference in the *bearing* friction, but that is definitely easily swamped by even the smallest difference in aero drag.
Back on the topic of the Aptera -- I think the most important concepts it illustrates is taking an "ideal" central shape, and then adding the wheels to that. The Edison2 VLC is a 4 wheeled example of this approach.
Another aspect of the Aptera that is interesting is the "beaver tail" -- this provides visual width, but the doesn't take advantage of the taper that is possible on the sides. The top and the sides of a vehicle can have greater angles on the closing slope; whereas the bottom is more limited in the angle by the fact that the air flow back underneath is limited by the ground itself.
The Edison2 VLC is a "fish tail" and since it has 4 wheels the width is provided by the wheel fairings. By the way, the "old" SAE Cd number for the Edison2 VLC is 0.145, so that is what we would compare to the Aptera numbers. Though, the Edison2 number is "real" and measured in the GM wind tunnel, while as far as i know the Aptera number is from CFD. The current SAE standard Cd of the Edison2 VLC is 0.161, and the frontal area is 1.7082 square meters.
On both the Aptera 2e and the Edison2 VLC, I am interested in the interaction of the air flow between the multiple shape volumes. When the Aptera 2e went to the front wheel drive, the wheel fairings got a lot closer together, and this along with the lower underside may well have account for much of the increase from Cd of 0.11 up to 0.15. (The other obvious change is the exposed unfaired drive shafts.)
That brings up another interesting study: the Aptera 2e uses elongated 'A' arms which are shaped like airfoils so on the spinning drive shaft has significant drag. The Edison2 VLC has fixed struts which are fully faired, so if you think about it you are left to wonder how they have any suspension travel on the wheels. They do this with compact trailing arms on the front (which also have to pivot for steering) and with trailing arms in the rear that house a chain final drive.
Another aspect of exterior faired wheels that I didn't fully appreciate until I saw the Aptera and the Edison2 in person, while they are being driven; and that is the room required for the steering pivot on the front wheels. The trailing taper on the wheel fairing has to stay clear of the main chassis, and they stick out on the outside of the turn.
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