I guess "demeanor" might be the wrong word. It's mostly an eye contact and smile thing, certainly directed mostly at the ladies in the audience. Compare the Christine's Tune/Hot Burrito #1 clip(which was before his Jagger thing) with the Eagles' 73 BBC show and you may get an idea of the influence.
Was it? I don't know. I would think that a private letter of a recently deceased man which contained passages which were potentially insulting to his peers wouldn't be revealed so quickly. And besides, GP wasn't a "legend" yet, people didn't care so much what he thought. It's nowadays that you encounter that quote so often.