I've almost* always had good luck over-doing it a little. Not a ball gown, but if you have a dark blazer, it shouldn't hurt to wear it with a skirt and stockings or some dress pants. I think it shows respect to put in a little effort.
But I've interviewed folks in suits and ties, hoodies, and polo shirts. I've never heard someone comment on anyone's interview attire -- finding people who know their stuff is hard enough without worrying about their shirts.
Good luck!
*Exception: dress down some for a Nike interview. I felt uncomfortable walking around in fancy clothes.