I worry about the same, I am 5'4" too.I love mixtes. I seriously considered a SOMA Buena Vista before settling on my Achielle Oma. I'm 5'4" and found that mounting the mixte in a dress wasn't quite as...um...ladylike as it was on the loop frame. On the other hand, I do tend to be a klutz, so that was probably operator error rather than a problem with the bike!
Ooooh, this is a good idea. I uncovered a new dress I got, while a nice fit and flare shape, has lightweight fabric, so I had to keep holding it down. I only had a mile to ride, so it wasn't terrible, but I was thinking it might have to move to the no-on-the-bike pile.I don't use a dress guard. My dresses are mostly knee-length and an A-line cut, so they really couldn't blow back and get caught in the spokes. My coats also are either waist-length or tailored closer to the body, so I don't see an issue there either.
The best trick I've picked up about wearing skirts and dresses is about how you stop them from flying up. This is super simple: you just clip a binder clip or two to the hem to weight it down. Works perfectly. You just have to remember to take the binder clips off when you get to work!