Sorry to be late to this discussion, but after reading the comments, I'd like to point out that winning the World Cup doesn't boost the image of a domestic league. Brazil's NT has won the tournament 5 times and yet, the Brasileiro Série A isn't considered a destination league, so winning the World Cup won't catapult MLS into a destination league either.
how much disposable income does the brazilian population have vs the US? there's a reason euro teams dont go on preseason tours of brazil...and its not quality of play....