Profile for Nagisa

I have read through many forums getting the deal on the dress code at the Broadway productions, and see that it wildy varies. Im planning a big day/date and am taking my girlfriend to see "Chicago" and a fancy dinner (was looking at "One if by Land, Two if by Sea", any good? anything better?). I dont own a suit or tux, so was thinking that I could wear my Dress Blues (USMC)? Too much? I dont want to underdress, nor look like a fool. Thanks for the help, never been to New York before so lookin...