Fascinating thread. I think one thing that has been overlooked regarding the accessibility of Irish, as opposed to Scots, culture (as perceived by the multitude), is the fact that Hollywood fell in love with Irish romanticism.
Irish are perceived as having the gift of gab, and all that gab about fairies, little people, leprechans, etc. and black-haired, blue eyed boy-os charming the girls was for many years the stuff of Hollywood cinema fluff. Especially in the 40's and 50's, when the movies had greater impact than they have today, the "no Irish need apply" scenario was replaced by actors happily spouting "Sure and yer that lovely, ma cushla." Often musical numbers were thrown in with a race horse and a plucky short jockey, with a brogue you could cut with a knife, in the background.

In the 60's this was taken past absurdity right into the rank marketplace with the adverts for Irish Spring, a hand/body soap. 75 minutes worth of stereotypical movie making reduced to a 90 second commercial.

I'm half Irish, and I well remember the cache this gave me when I was a teenage folk singer. Now I'm all Scots, by marriage, a Ross...with no cache at all, Mel Gibson notwithstanding.