Definitely non-party days are more crowded at MK during party season. We have been in October the last 5 years. In our experience, party days definitely have much lower crowds, at least until the party goers start coming in at 4:00 p.m. The non-party days are usually crowded because they are the days of the week that the park has longer hours for non-party goers and the only time the regular fireworks and evening parade appear and there is any MK evening entertainment for non-party goers. Now, there may be a little difference this year because the night parade is gone, but there is still the fireworks issue. Wednesday also has extra magic hours until 11:00 p.m. I think, so that tends to draw bigger crowds for the day as well. Basically, the day after the party on a non-party day, you have a ton of people who do not have hoppers and did not want to go to MK on a day when they had to leave by 7:00 p.m. (and in our experience the CMs start kind of "encouraging" people toward the exit around 6:00 p.m.- we saw an almost knock down drag out around 6:20 or 6:30 when the CMs would not let people without wristbands go down the New Fantasyland path towards the Ariel ride stating that the park was closing and they needed to move back towards the entrance- the people were very angry because they still had 30 minutes before close and wanted to ride Ariel).