I have only played the demo (a lot), but in the course of various games, I noticed that there is the same background image for the single A, and double A levels.
I would think it would be a real nice touch if each level had a different background image. Like, a single-A team would look like about the same as it does now, a double-A team would probably look similar. A triple-A team should have a larger stadium, maybe with a nicer-looking avatar for Larry's Workout thing, a bit of a skyline in the distance. And the big show should look like a major city with a big ol' 60,000 seat baseball stadium and a freeway and stuff.
Or maybe I am just wishfully thinking.