The first instance is when you are borderline right for the role and can dance. For example, the other day I auditioned for Fame which takes place in h.s. in the 80s. Now, I am almost 5'9" which means I do NOT read as a high schooler. So in order to look the part, I wore tennis shoes a t-shirt and my hair in a ponytail. I dressed younger, like I was in high school, so that I would not be typed out immediately. So if someone is trying to look younger, older, more ethnic, less ethnic, shorter, taller, etc. then yes consider your outfit. However, if you cannot get the choreography this will not help you in the least.
The second instance is when the audition is for something so specific that it is well known what you should wear, i.e. The Rockettes, A Chorus Line, Mama Mia, Rock of Ages, etc. For the Rockettes and A Chorus Line you need to show up in a leotard, tights, and a heel. NOTHING else. Linda Haberman and Baayork Lee do not play and they do not want anything breaking up your lines like pants or *gasp* shorts. Baayork nearly had a heart attack when a girl wore shorts in her chorus line audition. For Mamma Mia they want you in street clothes, don't come in a leotard and a Laduca they will not appreciate it.
Those two instances are the primary cases where you need to craft a specific look for your audition, but again they will never make up for poor technique and if you are fantastic enough they won't keep you from getting hired. I have seen a girl in a unitard and ballet shoes make a Rockette cut simply because she was good, but that is the exception and not the rule and most of the time you will not be the exception. So, do not go out and buy anything for a specific audition. Make do with what you have and let's all focus on the dancing and not the fashion.