While it's difficult to say, my suspicion is that the Alpine would not outsell the 4C in the U.S. market. Fundamental attributes of the car may make it more appealing, but I doubt they would be sufficient to overcome the lack of brand presence (Apline or Renault), the related lack of dealership network, and crucially, looks.

Alfa presence in the US market, physically and psychologically, isn't strong but it exists. It's a name that resonates with American car enthusiasts in a way that Alpine does not. Plus, it's Italian. When was the last time a French sports car was sold in North America?

Aesthetics are obviously subjective, and I've never seen an Alpine in the flesh. Whether or not one finds the 4C beautiful, it's difficult to argue that it is not a striking car. It's a car that will draw attention from enthusiasts and non-enthusiasts alike. Alpine may draw a crowd at Cars & Coffee, but I don't think it will do the same at a stop light or parking lot other than from car dorks. For better or worse, a significant part of the American market that would interested in buying a light, mid-engine sports car from niche marque wants it to look the part.

If Alpine had the Alfa badge and looked like the 4C, I'd agree: it'd outsell the 4C. But it's advantages as a thing-to-drive are insufficient to overcome its marketing weakness relative to the 4C.