Yes, all the Tango Shows are shows and for tourists. The Milongas are for the dancers and there are a few that do not discourage people from coming to watch.
Carlos Gardel is a good show with a film describing the history of Tango etc. There are models of tangueros that have space for you to put your face for a photo-op (you get the picture ?) and the food is, as at most Tango shows, only fair and fairly pricey,
That said, my DH and I enjoy the Tango shows and have been most pleased with La Ventana as a full-on show. The show upstairs at the Cafe Tortoni is very nice (best to not order a meal, just a snack and drinks)
For more relaxed Tango with very good quality dancing and (usually) live music, we go to the Borges Center in the Gallerias Pacifico on Florida St. They are inexpensive, more of a lovely auditorium with many Portenos in attendance. You can do a search above for more info...and check out this link: http://www.ccborges.org.ar/indexi.htm
AVOID El Viejo Almacen....we hated it and they were so pushy of photos, drinks etc., that we were sorry to have gone.
There is also spontaneous tango in San Telmo on the Square on Sunday evenings. Nice. And in La Boca during the day.