Thank you all again for all the helpful tips, and RafKa for the latest. I will re-consider the Arg visa. I wasnt sure if it was worth just for the falls(though EZE is on my radar, cant happen this time). MAO is mainly for a ride on the amazon(thanks to hollywood/anaconda) and checking out indian village, more than the rainforest part(for lack of time).

ps: do you mean tours like http://www.toursbylocals.com/riofavelatour?