I doubt if male authors even think twice about what to wear. Most of them I've seen wear Levi's or jeans, a nice T-shirt or turtleneck and a jacket.
It's a bit different for a female author. One thing we always consider is that we don't wear the same outfit we wore to this bookstore, conference, writers group the last time we visited or spoke. If you do a lot of appearances this can be a problem.
I have a friend who when she's promoting a new book, puts together and outfit and that's what she wears at every event.
I don't like having pictures of me floating around on the web wearing the same outfit. And I do. In fact, the red and black and silver top that I wore to several events I also wore to my granddaughter's wedding. She wanted me to wear something red and that's all I had that would conform to her wedding colors.
There's always the chance at a big conference that you'll run into someone with the same outfit on that you are wearing. Yes, that's happened to me more than once. I even had an author email me and ask if I was going to wear a duplicate of hers to an upcoming mystery con.
There are a couple of cons that I go to every year and I really try to change my outfits around so I'm not wearing what I wore the year before. Not because I'm vain--far from it--but I know photos will be taken and I'd like to be seen in something different from the very last year--though it might be from a couple of years before. No one's going to remember--it's those dang pictures that show up on the Net.
I've been staring at my clothes and trying to figure out how I can change things up so what I have looks different than it did another time.
I have one friend who merely changes scarves and jewelry but wears the same suit everyday. That works for her--but I'd be sure to slop food or drink on the one and only outfit and I'd be a mess the rest of the time.
So, that's one dilemma. So what do you wear when you're appearing places you've been before? Does it matter to you?