Here's my criteria for determining whether a city or town is a worthwhile culinary destination.
Is there something unique to the city? Does the city have a dish that originated there that the city is famous for? For example, you have the Cheesesteak in Philadelphia, Chicago Red Hot, Buffalo Wings, etc. Or, is there a notable food that is grown or harvested in the region that the city is located? Food like cheese in Wisconsin, hard shell crabs in Maryland, or wine in Northern California. Maybe it's a kind of style or way of preparing well known dishes, like pizza in New York City, barbecue in Eastern North Carolina, or clam chowder in New England.
Does the city have a relatively high population of certain ethnic groups? Ethnic demographics affects a city's food scene in the following ways. First it will determine in part a restaurant's clientele. A Korean restaurant in a town with few Koreans will have mostly non-Koreans as customers. Likewise, the same restaurant in a city with a large Korean population will likely have mostly Koreans as customers. This in turn affects demand and supply. A predominantly Korean customer base will be more sensitive to price and quality, and will thus force a Korean restaurant to be "honest." A predominantly non-Korean customer base will be less sensitive to price and quality. So, a Korean restaurant with a predominantly non-Korean customer base can overcharge for mediocre food. If this is true, then a city with large ethnic group populations will have better ethnic food.
Cheap food includes street food, homestyle cooking methods like soul food and southern food, fast food, bar food, post-bar food, and pretty much anything else that you can usually get for around $10 or less. When I evaluate a city based on this criterion, I look for cheap eating establishments that are not chains. I look for food trucks or pop ups. This category is also tied up with ethnic cuisine, since a lot of great ethnic food will also be cheap.
This includes the fancy pants food in a city. This is basically any kind of dining experience that'll cost you at least $100 per person. Here it's usually about the chefs. Does the city have notable chefs doing all kinds of awesome things with food?
In my mind, only two cities in the United States score well in all four categories: New York City and Chicago. Most other cities don't really have anything that's uniquely indigenous to it, like Los Angeles, Seattle, Portland, Dallas, Phoenix, or Denver. Some cities are lacking in ethnic diversity, like San Antonio, Detroit, Minneapolis, or Boston (where are the Asians?). I might be wrong, though. Of course these measures are all relative. These cities will of course have a higher ethnic group population than small towns scattered across the US. Philadelphia, San Francisco, and Atlanta might contend for cities that score highly in all four categories.