Stumbled on this thread searching for something else, and noticed that the Kansas City "oldies" station that used to be "50's and 60's" --- is now "60's and 70's". Funny, the same image hot-link still works, just their logo has changed (well, that, and their format).
My bet is that the "50's and 60's" oldies stations are going the way of the Dodo bird, as did the "40's, 50's, and 60's" stations that existed as recently as 10 or 15 years ago. (I know, I worked on-air at an AM/FM set of sister stations while I was in college -- where the AM station was 40's, 50's and 60's.)
Up, for no good reason.
I had a conversation with a KCMO guy who was passing through this area. If I converse with him again I'll have to remember to ask him about this?