What I wear has a huge effect on my mood, self confidence, etc. (I don't mean to sound vain and I am certainly not a clothes horse.)
I think part of it has to do with the 'uniforms' we all wear in our daily lives. Think about the way people usually dress and the way we expect them to act. You wouldn't want to walk into a doctor's office and see him wearing a tux. You also probably wouln't see a car salesman wearing cut-off jeans and flip-flops at work.
You are using the leather to help you get into the mood. In a sense, you may be using it as a prop or even as a crutch. Once you have been playing for a while, the dress will seem less important (although you will probably still wear something that symbolizes your dominance).
For me, clothes have a lot to do with mood and mood is everything. I can be completely submissive or completely dominant in any situation if I am in the right mood for it. Otherwise, nada.
why do cops wear uniforms? why do judges wear robes?
not just so we can imagine stripping them off of them....
but I digress.
" Clothes make the man", or in your case the Domme. Dressing up is ritualistic, especially for femal;es who are taught to play dress up from early ages.