The Foursquare ad campaign to me is more intended to people that likes to take care of them selves and likes to dress up such as hipsters. I feel that Foursquare ads are mostly shot in nicest places like the park or a restaurant. The ads are more serious and straight to the point. Meanwhile in the Yelp ads we see more variety of environment and the ads let you imagine what they are promoting. Yelp is targeting everyone and we can tell that right away because their ads are funny and they show more variety of people. If I had to chose between the two apps I most definitely chose Yelp because I can relate more to it.
I think you are right that the foursquare campaign aims at an upscale audience or at least people who want to be upscale. The humor in the Yelp campaign appeals more broadly.