Matthew: There is an excellent book by Peter Kohler, called the Lido Fleet, which details the whole Italia story. Basically, what happened was that although Italia maintained good (by the diminished standards of the early 1970s) passenger totals, they were plagued with A) an extremely popular but aging flagship (Cristoforo Colombo) B) an extremely popular but horribly costly to operate flagship (Leonardo DaVinci) and C) twin superliners which did not "click" with the travelling public and, like the Normandie, were generally only half full. Add to that, Union difficulties, loss of government support, the maintainance of a three class sytem aboard the liners well into the day of "one class only" cruises, and the fact that the cruise revolution was still about 5 years in the future. Italia folded in 1976, 'though its successor survived a year or two longer.
I think that of all the "classic era" lines, Italia could stand the best chance of being revived, 'though not entirely in the American market. If they were to offer a competitive NYC/Genoa airfare, the same standards of food, service and accomodation was was offered pre 1976, and keep their ships on what was referred to in the 1960s and '70s as the "Med-Go-Round" they would be on to a winner- particularly if they offered both 7 and 14 day voyages.