You could always do a theme - like Tarts and Vicars but with more Halloween flare - Vamps and Vixens? Witches and Wizards? That way they know more or less what they are aiming for, now they just need the actual costume. I believe that most people, once they experience the costume party full-on, will look forward to it next year!

Leigh Clements
The Mystery Maiden
Shot In The Dark Mysteries.com