Hi Sheryl,
Thank you for stopping by the Disney Parks Moms Panel with your question. Visiting Magic Kingdom Park is always magical, but there are definitely some options to weigh if you are considering visiting the Theme Park on days where Magic Kingdom Park closes early for a Special Event such as
Mickey's Not-So-Scary Halloween Party.
I have never noticed a difference in crowds when visiting Magic Kingdom during the day prior to the Special Event. Although the crowd levels aren't really any different, your time in the Theme Park will be cut short, since Magic Kingdom Park closes early for guests not attending Mickey's Not-So-Scary Halloween Party. If you plan on leaving early, then the closure shouldn't affect your visit, but if you were planning on staying until later in the evening or watching Happily Ever After, the new Fireworks Showcase, you may want to choose to visit on another day.
One thing I have noticed in the past is that transportation to and from Magic Kingdom, as well as the front entrance can be crowded during the crossover period from around 3:30 pm until around 7:00. Guests without tickets are leaving Magic Kingdom Park while the guests coming for Mickey's Not-So-Scary Halloween Party are lining up to enter Magic Kingdom Park, causing longer lines and wait times for transportation.
Personally, on days when I know there will be a Special Event that I am not attending, I will always choose another Theme Park, mostly because I don't want to feel rushed knowing that the Theme Park will close early. I like being able to leisurely enjoy the Theme Parks into the evening, without having to stick to a specific timeframe.
I hope that helps, Sheryl. Please let us know if you have any other questions!
Stephanie