I can find little hard data but as an Italian-American that grew up on the Jersey Shore and lives fairly close still I wanted to clear up some confusion.
In general the Guido of today is not the Guido of yesteryear. It was a more generic term of derision for Italian-Americans of lower classes and perhaps associated with Guinea Tee* and Gold Chain Wearing types or the black socks, sandals and shorts visitors to the Jersey Shore that were a subset of the Bennies2. Jon Travolta's characters in the 70s could have been called a Guido.
Today's Guido is a new but related and better defined subset of Italian-Americans that are yet another generation or two removed from their immigrant forebears. They are mostly from Staten Island and simply visit the Jersey Shore in the summer and few are actually New Jersey residents. Oddly enough last week the local Public Radio station WNYC had a small segment about the Guidos.
* The sleeveless ribbed undershirt also known as the wife-beater.
2 A derisive term for the bad drivers or obnoxious New Yorkers that flood the Jersey Shore every summer. (Non-ethnic)