My son and a friend did the MK on a party night this past Monday. It was packed. The crowd level predicted was a 6, but actual crowd ended up being a 8. They had a great time, though. Had dinner at Casey's corner, did shopping/browsing around Main Street USA, watched HEA at 9. Many people left after the first fireworks show, but they stayed as they heard that they were doing a second Fireworks Show (once upon a time) at 9:45, so they watched that.
Expect heavy crowds, but if you can handle it why not.
Last Saturday, touring plan predictions were off too (underestimated) -- actual crowds were recorded for a 10 for this non-party night (original estimate was an 8) -- end of Jersey week. A 10 in November. Crazy. None of us were there to experience that, though.
DS was originally pretty excited to be touring on what would supposedly be a crowd level 6 day with some pretty reasonable waits for things he didn't have FP for, but soon found out that touring plan original predictions were off, standby lines were longer, and ended up switching fastpasses around to do some must dos and skipped some other things. (e.g. gave up a peter pan fastpass - did not care that much about that to get one for Pirates that DS's friend really wanted to do and had a stand by line much greater than predictions. Skipped Peter Pan, Big Thunder, Jungle Cruise, and It's a Small World as lines were longer than what they were worth stand by. // not going there to do attractions is what makes plans doable for you. DS and friend made the mistake of waiting for 7DMT (wait of almost two hours) originally predicted to be 38 minute. After that they stuck to lines under 25 minutes for standby. They'd still rate their experience a 10 out of 10. But an eight crowd level vs. a 6 really is a big change in lines waits. The MK, though, is a fun place to take in just wandering around, etc. These two young 20 somethings enjoyed the parade, show, browsing gift shops, and two fireworks shows for sure.