I visited Vegacy on a recent trip to Brazil (March 2015) and was impressed. The buffet offered a per kilo option on a Saturday afternoon, and the price was very reasonable. The food was generally tasty, although I didn't care for the beet balls (my own personal taste - my dining partner loved them). The salad was fresh and there were several hot foods in the buffet. They had some delicious chocolate truffles, also vegan. I wanted to go back to try the soja burgers but didn't have time this trip--will definitely visit it again on my next trip to Sao Paulo. I highly recommend this restaurant. It was a little hard to find and we walked right by it before realizing that it's on the second floor and the entrance is a flight of stairs. The hours listed on the Happy Cow site may not be correct - when we were there it closed at 4 pm on a Saturday, not 6, so check.
Cons: Not open for dinner