We did it last year and had a fabulous time but I have to say absolutely dress up but LIGHTLY!
It was so humid that my hubby had to go back to the room early, he just couldn't cool down. My ds was overheated as well.
The trick or treating is a blast and the fireworks and shows are unbelievable. You'll see so many more characters than normal.
One good thing to do is bring some of those glow sticks. It's very dark at night in the parks.
My family dressed up as pirates but there was a little bit of everything from Spiderman to Jack the Pumpkin King.
Just have fun with it and don't invest in a ton of money for it. Go to Value Village or Goodwill and piece together something if you can. Then if you don't want to bring it home with you on the plane, you can leave it.