Here are some other things I can think of...
- Attend a Futbol (Soccer) match
- watch Polo (during the season)
- wander around San Telmo when the "feria" in on duty
- visit Cafe Tortoni and walk down Av. de Mayo
- walk around Plaza de Mayo and Puerto Madero
- visit the Teatro Colon (guided tour)
- eat lots of dead cow and drink the local Spoof Juice...

- visit Recoleta Cementery
- walk around Caminito & historic La Boca
- see the change of the guard by Los Granaderos at Plaza de Mayo
- visit the Rose Gardens and Parks of Palermo