I think there is always a craze for the music of 20 years earlier. When I was a kid in the 80's, everybody was going on about the 60's and so on.
Also, Happy Days was very popular then. The Fonz has a lot to answer for!
No, Happy Days was much later (1976/7). I think one of the influences was the 1973 David Essex film That'll Be The Day. The first retro Rock and Roll hit I can think of is California Man by The Move in 1972. Can anyone think of an earlier one?