My guess is that it would be very difficult to be successful boarding a flight that has Brazil as your final destination without a valid visa. If you had a layover there, no issue. But if Brazil is the last stop on the itinerary they probably won't let you board the plane with just a "Don't worry, I'm just gonna hang around in the terminal." line.
Brazil's visa policy is based 100% on reciprocity. They will only require what the other country requires of Brazilians. Last year (or the end of '13, I can't remember) Mexico dropped visa requirements for Brazilians whose trips were tourist in nature. Brazil immediately dropped those same requirements for Mexicans wanting to visit Brazil. When the US changes their policy towards Brazilian tourists, Brazil will follow suit rather quickly.