Seldom are my meals at a Sanborns particularly memorable, but they've always been reliable. Depending on their location, they serve as a place to have a quiet and comfy seat (in a mall, for example), find relief from the heat, and/or to pick up books, magazines, maps, postcards, etc. In some locations the ambience is a combination of the atmosphere at Denny's, Sears, and Starbucks.
I did have an interesting Thanksgiving turkey dinner at the Sanborns in Col. Lindavista (northern part of el D.F.) on year at my local niece's instigation. All I could think of was that turkey would be better served (on either side of the border) in a classic mole sauce.
La Casa de los Azulejos has the oldest Sanborns in the chain (I believe), and it is worth the time checking it out for its tile work, especially if you're anywhere nearby.