We've been to it 4, maybe 5 times I think.
The first few times we seriously dressed up, but the oppressive heat and crowds kind of did us in. I can't say I recommend wearing really serious costumes in Florida in September/October, even at night, unless you are doing a character that intentionally is not covered much (i.e. Tink or similar).
The last time we just wore Disney Halloween tshirts from various prior years, and had a much easier time of it. I did buy one of the little Nightmare Before Christmas headbands, looks like a little striped top hat with a silver spider and some feather fluff, and wore that too.
The vast majority of the people there will just be wearing whatever normal clothes, though. My estimate is that perhaps 10-15 percent of the adults actually wear a real full-on costume. (My hat's off to the ladies who go full Maleficent - only their faces and hands are uncovered, that has to be SO HOT to wear!)
And then perhaps another 10-15 percent are doing what amounts to DisneyBound, where they just pick colored clothes similar to a character and add face paint or whatever.
If you do the DisneyBound type thing, you can at least stick to shorts and tshirts and not be so smothered by costuming.