The battlefield isn't really that overrun with commercialism. The only problem is the town, which existed at the time of the battle. You really can't expect the town to have ceased its existence or be frozen in time for 140 years. The main parts of the battlefield from the second and third days are pretty untouched, and even the first day areas aren't bad until you get in the town itself.
I expect commercialism. It's the American way. People have to eat somewhere *lol*