Here's a quick review a few more things I did in Argentina art related:
Visited Museo Nacional de Bellas Artes (MNBA). A good traditional and modern art museum combined. I spent too long on the lower level and not enough on the upper one, but a good way to spend an afternoon. Famous European Artists below and Latin American artists above.
Visited Museo de Arte Latinoamercano de Buenos Aires (MALBA). A GREAT modern art museum. Loved it. Lots of funky pieces. Lots of fun.
Saw 2 live theater performances at the Cultural de la Cooperación Floreal Gorini for more or less $10 each (35 Argentine pesos). One very good, one very confusing. One I could follow, the other hopeless. One a story arc, the other crazy people on stage ranting about...well, I don't even know. El Tiempo y los Conway and Los Siete Locos
Saw a movie. Although a German film with Spanish subtitles, still very good. And Along Came Tourists
In review, if you plan on going to Buenos Aires you have to partake in the local art scene. Definitely go to a live performance and definitely pick a few of the art museums and visit the ones you think you'd like the most.