New York magazine listed how much people spend per month to eat out. The highest rate in the city was singles nightlife Chelsea-Clinton: $754–$2,398. If we look at some neighborhoods with large numbers of Jews, notice the differences:
Upper West Side: $709–$1,056
Williamsburg-Bushwick: $56–$80
Borough Park: $116–$193
East Flatbush–Flatbush: $48–$237
Bronx- Kingsbridge–Riverdale: $300–$444
For comparison purposes it does not matter if the Hasidim or the Hipsters of WIlliamsburg are at the high end becuase either amount is below Boro Park. Do people regulate their eating out based on their religion or does their available income determine their religiosity? Does eating out as part of one’s life change one’s religion? Why does it line up so predictably? What is the correlation of religion and dining out?
The Book of Doctrines and Opinions: 
There is a correlation between income level and dining out. To the extent that there is a correlation between income level and religious practice, that might be relevant.
Far too many unexplored variables to make this a worthwhile study on its own, IMHO, and of course, there’s always the important caveat about correlation and causation.
Assuming that there is a correlation between religiosity and income level, it’s probably at least just as valid to say that the former determines the latter (i.e., more “frum” Jews eschew money-making opportunities, have larger families and hence less discretionary income, etc.)
It might also be interesting to survey how often people dine out as related to how much they spend. It’s quite possible, for example, that religious families go out to eat no more than their non-religious counterparts, but due to (a) higher price of kosher food, and (b) larger number of mouths to feed, they wind up spending proportionally more per trip.
I think there is more here than economics. a generation or two ago kashrut created a culture in most locales of eating only at home. Now eating out at the local kosher eatery has real social/cultural significance. note the controversies in various frum communities about the appropriateness/value of a Kosher pizza place. I have heard people in Alon shvut say they are glad there is no pizza there like in efrat.
The financial and identity issues are always present. Eating out costs money.
Additionally, not eating out or eating out fosters an identity which is a mixture of religion/class/education/etc.
There is also the social aspect of eating out. Stay-at-home mothers in Borough Park & Flatbush
socialize at pizza shops. Singles on the West Side at the Pizza Stores etc.
It is, for some, an alternative to Synagogues as a center for community, etc.