That's my use case for yelp like sites anyway. When I'm at home I go out for dinner on avg. once or twice a week or so and go to a new restaurant probably less than 1 time in 10, so my need for restaurant reviews is quite low. I also have plenty of other local sources for good reviews when I need them

When I'm traveling I eat out basically every night and visit a new restaurant pretty close 100% of the time. On the whole I have much greater need for a site with reviews of restaurants in not my home town than in my home town, and that hardly seems niche to me.