I don't think Miami is going to work. Putting pro sports in Florida always sounds great, but Florida sports fans are interested in three things: the northern team from the city they grew up in, college football, and why the NFL won't give Tebow a chance. I do think it could do well in Minneapolis, St Louis, Detroit, and a few mid-sized cities that don't have multiple pro teams now.
Atlanta and Houston are pretty similar. When you're winning, we've loved you forever. When you're not, we forget you exist. And either way, we care about pro football more than anything else. I'd like the MLS to grow, so maybe I should support the Dynamo, but I really don't. I have become a pretty committed EPL viewer, if that counts for anything.