We did, mostly because our kids were into ALL of us doing it. We didn't do full-on Halloween type costumes though. DH cut off a pair of cheap sweatpants, wore a hideous medallion-pattern shirt from Goodwill and a leather vest (also Goodwill) and flip flops. (He did end up going to the gift shop on the Magic for some accessories, though, b/c without it he just looked like he'd fallen into a really unfortunate bag of laundry). I wanted to turn "real" clothes (that I could wear in real life) into something pirate-y looking. I wore red denim capris; a top with flowy sleeves from the Banana Republic Outlet; a denim vest (Goodwill); a yellow scarf I already had, tied as a waist sash; giant gold hoop earrings (the biggest and cheapest I could find at Target); and a big brass key ($2 at Michaels) on a long necklace chain, and black flats.
When we went to dinner (first seating) we didn't really see any other adults dressed up... but by the time we left dinner, we saw a bunch of people more dressed up than we were!!