The SEC is a very homogenous league outside Vanderbilt, which is one of the preeminent schools in the country with a campus that still feels very SEC despite the fact that it's in the middle of a big city. SEC has shown an eye towards maximizing new markets, like everyone else, but they certainly haven't neglected to make sure their expansion has made sense and fits culturally into the rest of the league. I would say SEC has done the best of that hands down to this point. The SEC's ability to be incredibly selective to whom they extend a membership offer is their trump card.
Texas A&M and Missouri fit better culturally into the SEC than Rutgers does in the Big Ten, by far.