The Shriners in Denver have a Medieval Feast every year as a fund raiser. Half the people attending wear their kilts- both great and modern. I doubt much of anyone will know the difference, and if they do, they'll appreciate that you at least made the effort, and will think no less of you. I'd say do it.

***EDIT*** Just read the thread a little more closely. Is a Medieval Times dinner a dinner at a restaurant? If so... then disregard my advice...