From first hand experience, treating such occasions as a license to crossdress doesn't remotely do some of us or our motivations to crossdress any justice. I've grasped at this straw on quite a few occasions that weren't Halloween, thinking I was making the best of it. It wasn't even close, it felt crude, it felt empty.
If I want to crossdress I'll do it at my own will - I don't really need the license of being able to be out in costume, much as I am willing to take advantage of it. If I want to obscure my shape I may as well wear garments that create my silhouette, like historic gowns / "princess dresses" or even a milk carton.
I'll admit lazily compiling a pilot's uniform out of my own drab wardrobe (save the peaked cap and wings, both actual costume items) for Halloween while I was spending it overseas. I will definitely go for a showgirl costume eventually, and for more occasions than just Halloween alone.
