We have gone once on Halloween. It was our first year as APs back in 2014 and it was definitely true then, that Halloween Eve at DLR was a ghost town (our party was also a rainy one, so they didn’t do the cavalcade or any of the dance parties but we still had a great time)!
I imagine, that the party may be popular, but because DLR doesn’t allow adults who aren’t at the party to dress up, it’s probably not going to be a destination to take place of Halloween festivities for the night. But it may be a place people who don’t love to celebrate Halloween may head to for the night, but I would expect a moderate day/night still, since it will be the last night in DL for most of the Halloween decor. It’s wild how much of it will be down the next day, literally overnight.
I’ve found this to be true at pretty much every Halloween thing on actual Halloween… I’ve been at WDW on Halloween a couple of times and other than the week after Labor Day it’s the only time I’ve seen a true 1-2 CL at MK & HS. It was funny the first time, because we were going to MK before party time and had been worried about not making it back to OKW in time for the staff golf cart parade & trick or treat (they decorate all of the golf carts, get dressed up and ride them through the resort, then park at the poolside and hand out candy to the kids… they usually have a couple of characters, and then they show Hocus Pocus), but it was so dead in the park that day that we were finished by about 2pm!
I always love that changeover… I was at Universal on year when they ended HHN on like 11/2, and the very next day there were Christmas decorations going up!