I have never been there but will be going to the party 10/24. From what I understand, since the party tickets are limited, the crowds will be quite lower than the day. Even if the parties are sold out, it should not compare to a normal night at Disney.
I will also say that I normally go during Easter week, one of the busier weeks at Disney and if I go after 11 for one of the EMHs, they are not usually that crowded. So if I can handle the EMH crowds at Easter, I can handle the ticketed party crowds.
The only time I could see it becoming crazy would be around 7 when the start closing the parks.
Anyone with a more knowledgeable opinion would be appreciated. With going this Thursday, I am interested in the crowd level too.