Star Trek collector card with Tonya as Fire Sculptor
Here's another interesting tie-in!
Having been a Con goer, a Renn Fair junkie, SCA member, and belly dancer...
I'd wear normal business style clothes and beautiful make-up with some fantastic Middle Eastern jewelry for the lecture. Authors and other lecturers have worn professional clothing at the Cons I've been to which were on the East Coast. I don't know what they wear on the West Coast, but you might ask around. I think you will have enough warm bodies in costumes.
To set the hook, maybe start out with a light hearted look at belly dance in popular American culture. (Star Trek, ATS, Harem girls, Gor, etc.) Then jump into dispelling the myths about how they came about. Then give them the real history.
Remember that a lot of people there take their personal fantasy ideals very seriously. You don't want to alienate (HA) your audience by telling them right off the bat, "Hey, you're wrong!" Identify with the Con culture, validate their 'play aspect" (if you are comfortable doing that), then tell them the truth about the origins. The important thing is to get people to listen. I hope you have a great time!