I think you sell yourself short when you say ">As a professional dancer, I would have to say "no", my costume doesn't really improve my performance."
I have know a few professional dancers in my time, and understand fully what you say about the concentration needed on stage. I would bet that you are able to take on the "character" that you're dancing, but maybe you don't realize that, because it comes naturally to you. Why the bet? Because once you achieve a professional status in dance, to me it means that the producers, directors and choreographers select you for your performance talent. If I may be so bold, you wouldn't have the success you've achieved without becoming the person that the costume is made to fit.
Maybe the actual physical material of the costume may come after you've become the "costume" of the personality, and in that sense doesn't add to character you've already accepted. But achieving the level of professional in dance means you have the ability to be the character you perform.
You also make an excellent point that I wish I had said. There is so much more to becoming a character on stage than just wearing a costume and dancing. The stage is a complex traffic jam of performers and does require a great deal of awareness that many "casual" dancers may not understand.
balletboy[/i]