Author Jeremy Donovan's in depth study of World Champion speakers suggests when you first look at your speech before deciding whether or not you want to wear a costume onstage. Look in your speech for the setting and background of your stories and see if wearing a costume would help strengthen the setting and background for your audience (e.g., you wear a heavy coat and hat when you talk about being trapped in the snow for hours).
Looking,
Looking,
Tim Wilson
Professional Speech Coach
Free speaking tips at: http://speakingquicktips.blogspot.com