You will just LOVE seeing the Executive Headquarters!! I went for the first time this February (for Firesides) and cannot wait to go back.
I would definitely call ahead and make an appointment. That way you are assured of visiting at a time when it is open and people are available to show you around. When I was there, we did wear pin attire, but I don't think you would have to just for a regular day--I would definitely wear nice pants and shirt though--no jeans, shorts, or short skirts. After all, there will be a lot of great photo opportunities and you want to look your best!!
Have a wonderful time, and don't spend too much at Chi-O Creations!!