I think Jack Swagger should keep his All-American American gimmick. I don't think the gimmick is a problem. I think he needs a face turn just to test the waters a bit. His All-American American gimmick is much more marketable as a face type character than a heel. Plus, since he currently isn't doing anything currently, a face turn would desperately give him something to do. Right now, I just don't see how he can be a big deal as a heel right now in the mist of fascinating heels like Daniel Bryan and Dolph Ziggler.
If WWE doesn't want to turn him face and they don't have much faith in a face turn, than yeah. He would need to get a drastic change. You can't market his All-American American gimmick as a heel because it's not getting him heel heat at the moment. Making him more aggressive and vicious may work given his strength and his size. Changing his look along with his entrance theme will also need to happen in order for him to gain momentum as a heel.
I still believe that Jack Swagger can be a main eventer but it's going to take some time. Nothing happens overnight and if you try to push someone that isn't ready yet, it isn't going to work out. WWE learned that the hard way when they put the World Heavyweight title on Swagger 2 years ago. If they can hide his weaknesses and expose his strengths with his character, than maybe things will go good for Swagger. I was a fan of Jack Swagger ever since his WWECW days. His ECW title reign was wonderful, especially his first in-ring encounter with John Cena on Raw 3 years ago. It would be a shame if his talents go to waste.
By the way, congrats to Swagger for granting his first wish.