The four of us went to Mexico City for Ariana's script research and for a pleasant vacation. Mexico City is a very interesting place: huge, dirty, smelly, lots of poverty, and very foreign to us. But very interesting as well, and while I don't think we'd go back very soon, we did have a great time.
As far as logistics, we stayed in the Holiday Inn Zócalo, which is indeed that kind of Holiday Inn, but not at all like the chain we know and hate from the US. It was clean and reasonably priced, and relatively quiet. We had considered staying at the Gran Hotel Ciudad de Mexico a couple of blocks away, but some of the reviews mentioning noise from weddings in the atrium (which has a gorgeous Tiffany glass ceiling) scared us away -- fortunately, since there were, apparently, such events while we were in town.
There was lots of Mexican food, oddly enough, and we didn't try to find a whole lot else, though we did find a creprerie that served us several lunches and breakfasts. In addition there was a restaurant next to the hotel that was really excellent. It is called Mercaderes at 57 Cinco de Mayo. Be sure to order the duck in pear chipotle sauce.