Your mention of nudist magazines brings back memories. As you say- before 1970, magazines couldn't show genitals unless it was for "instructional" or "educational" purposes. Well some court ruling said that magazines about nudism were for "educational" purposes and exempt from the ban so 1960s magazine stands were full of big glossy nudist magazines which would make you think that half the people in America were nudists and most of them beautiful young women!
Anyway- after the Penthouse ruling these nudists magazines practically vanished overnight showing what they were largely being bought for. Nevertheless, they had inspired many young people to become interested in nudism which was very popular in the late 1960s and '70s but now that these magazines are gone this valuable recruitment tool has been lost so nudism is literally dying from old age now with hardly any young people entering to replace the old ones.