Down and Delirious in Mexico City is definitely an interesting read, but IMHO it is more about the seamy-side youth culture here (goths, emos, latter-day hippies, etc) than it is about what most retirement-age folks want to know about the city.
I found it to be not as interesting and not as well-written as David Lida's First Stop in the New World, which is a marvelously fascinating collection of stories about where to go (and where to stay far away from!) in Mexico City.
For me, Hernández's book was a struggle to read. Lida's book was a struggle to put down.