I went to San Antonio de Areco on the recommendations of many BsAs residents. To be honest, I didn't see what all the fuss was about. It is a nice enough town, but certainly doesn't live up to the fuss people make of it. It is quite tranquil as it is a small town, but apart from a short walk along the river (pictured in my profile pic) and 30 minutes spent at the Gaucho museum there really aren't any other tourist activities.
Something else to keep in mind is that San Antonio de Areco has a five hour siesta so most places (including most restaurants) are closed between 12pm and 5pm which could make a day trip there a little hard.