Aerodynamics isn’t that big a deal. At normal highway speeds, good vs bad aerodynamics might give you ±2-3 mpg. Stacking a bunch of bikes on your roof (terrible!) and hitting 100 mph, you might half your mileage. But most vehicles (even older ones) have enough of a decent aerodynamic design that all you can really do is make small improvements that aren’t that noticeable. Underinflated tires is going to do more damage to your numbers.
And really, would you rather have a badass looking Mustang or Corvette from the 60s (obviously with today’s improved engines and all), or the sleek-ish all-look-alike ones from today? Can a non-car guy even tell the difference between the Camaro or the Charger or the Challenger or even the Mustang?
One of my daughter’s boyfriends in HS, early 2000’s, thought our ‘98 Firebird was a Corvette.............