I definitely really like it when people come back with more thoughts after an interview. Accounting for nervousness is always a difficult thing to do, but important. Definitely the stories in this whole thread about people who were told they weren't "confident enough" imply people not taking this into account.
On the other hand, I was once involved in hiring someone who we thought was nervous but it turned out the signs of nerves we were seeing were probably DTs. They didn't last very long for mostly unrelated reasons, though it's possible we could have done better by them as well. Still, it's sometimes hard to parse out what even looks like nerves in an interview because it's usually treated as such an adversarial process.
Mostly these days I try to focus on making it feel less adversarial when I interview, to try to get people over that nervousness and treat it more as a conversation. It's amazing how far you have to go to convince people you're not trying to trick them though, because of how many standard interview questions are (intentionally or not) trick questions.