I'm younger than Joni Mitchell but I also wore my hair straight and dressed in long dresses in the early 1970's. My parents probably still have the Kodak pictures to prove it.
The YouTube videos reminded me of how often women wore dresses when I was growing up. I still wear a dress or skirt about once a week to work. Most of my co-workers that have a similar job wear jeans or khaki pants on a daily basis. Even on Easter or Christmas in church, I see very few, if any, women wearing a skirt or dress.