when i'm going to check out a barn i'm usually in my breeches and paddock boots, but that is because i'm stopping in at that barn on either my way to or from where i do currently ride.
i find some barns and their staff around here are more amicable and talkative with somebody visiting/stopping by when that person 'looks the part', but it really doesn't matter in the long run, as what you say and how you act is the true measure of yourself, not the clothes you wear.
when i went out for the test ride on my new lease horse last week, i was wearing jeans, paddock boots, and the same 'office-y' shirt/blouse i wore to work that day. yet when i ride i usually wear breeches. didn't matter a bit to the horse's owner what i was wearing, he was looking at how i rode and how i interacted with his horse and himself.