I have seen the idea suggested, and I think there was one site that did mystery cities, but I hadn't seen a combination like this one, where you depart from Madrid or Barcelona, and end up in one of several cities, with a hotel at your chosen star level, for a 2-night stay.

http://es.groupalia.com/descuentos-g...hes-hotel.html

My feeling is that this would not work so well in the United States, due to the lower density of appealing cities to visit on a short flight (in most areas). But it is definitely an interesting idea.