As a Buffalo native, I can say that chicken wings (NEVER “Buffalo wings”) became commonplace in the area around the mid-1970s – every pizzeria served 'em. (Buffalo-style pizza is a phenomenon for another thread.) They spread north first, to Buffalo’s “cottage country” along the Canadian shore of Lake Erie, then up the QEW – I remember my first sighting in Toronto around 1982 or 1983. There’s more Toronto-Buffalo interaction than Rochester-Buffalo interaction – wings were slow to spread eastbound on the Thruway, but they finally became commonplace in Rochester in the late 1980s.
There was probably some point when wings hit critical mass, from being a local specialty to a regional food to a national phenomenon. Why wings, and not lutefisk or Rocky Mountain oysters or some other local delicacy, I don’t know.