Once again, I have to agree with Randr7896. (Perhaps he and I married sisters? lol)
We began the hotwife dynamics a couple of years ago and I did not notice a change, (other than the obvious taste difference, right after and the feeling of another man's cum inside of her as I entered her).
But for the last 2 months, my wife has had a regular (once midweek and once on the weekend) with her new guy. I did see his cock the first time that they were together, and he is significantly larger than me, both length and girth.
I now notice that her outer lips are more distended and "meatier", if that makes sense. When I enter her, the walls of her vagina seem to very lightly rub my dick, as opposed to gripping me. I just sort of enter her and yes, I too feel small, even though I'm as hard as I've ever been.
The real treat for me is when on a rare occasion, I get to see her immediately after He has pulled out. My wife is still gaping and full of His cum!
And yes, this vulva/vagina transformation is also a huge turn-on for us both!