Sunday in the park with Ana Sabrina's divine tacos is still my favourite thing to do before I go to feed my chickens around the corner. But this summer (2013) the old arcades were renovated and new shops and restaurants have moved in and it's a lively place to dine alfresco at night. La Tratto is an American Bistro with the kind of safe food you'd find in any American mall. It is generic fare with no flare but it's a nice setting and you can dine or drink alfresco. If they would cook the pizza in a hotter oven it would be crisp and enjoyable. Much better food can be found across the park at Apaola the new Oaxacan restaurant. Apoala is my favorite place at the moment and I've not experience the awful service and delayed meals I keep hearing about. I like the appetisers much more than the main courses.
Having grown up in rural Texas where we had to drive ten miles to find a Dairy Queen I was appalled when one turned up with it's unfortunate signage in the arcades of Santa Lucia. Since then I've come to regret the Butterfinger Blizzards and dipped cones even more. Ki Xocolatil has a new location in the corner of the park and this is where you should have your coffee and sugar fix.
Sunday afternoons there's dancing and live music. Thursday night there is a folkloric dance concert. Both can be very loud...ear plugs are de rigueur!
Update November 2014
I personally think that Apoala is the best restaurant by far in centro. The wait staff is now experienced and efficient. The kitchen is now working twice as hard as before as the restaurant is always full and you'll need a reservation most nights if you go at prime time around 9 but not if you go early or late.
La Recova is a Argentine grill that I quit going to many years ago up north but they have just opened on the corner of the arcade. In fact they have barricaded the passage of the arcade and constructed 3 or 4 hideous obtrusive gazebos and taken over the south side of the park. They have totally ruined the ambiance of the park. I do hope they fail and soon.
Soon to open is a tapas bar called Bottela Verde a great idea in a tiny little corner... more updates soon.