I love the idea of a 70's fest, but the artists shouldn't sing their current repertoire, they should sing the songs that were in their sets then or were the current favourites in the clubs.
"Hey Sandy", "Cursed Anna". I'm sure you have total recall if you were around then. You could have a 60's fest with the songs everyone was singing at that time, it's easy to do the research, but there would be no point just booking the acts to do what they do now, that would just be another festival.
If folk means anything it means preserving the best of the past and there was a lot of great stuff back then that the young don't know and don't seem to care about. Time for a revival I say.
And no cheap ageist jibes about clothes, fashions, etc please. It's been said before.