If you have park hoppers or don't mind a short day leaving at 3:30 p.m. a non-party day is really great and much lower crowd wise. For our November trip, the non-party days (already predicted to have significantly higher crowds that party days) were heavier than in past years and significantly greater than touring plan crowd predictions (and they are pretty good at their predictions normally). We one time did a non-party day from rope drop to 3 p.m. Except for the line for lunch at the Beauty and the Beast castle (new popular dining experience at that time) which was ridiculous, it was walk on or 20 minute or less waits for almost everything.
There may be a lot of people like my family out there that aren't that enamored with the parties (been there, done that, bought the T-shirt), don't have park hoppers, and want to go to the MK one and only one day on an Orlando trip and do both rope drop and fireworks. I'm personally not into the fireworks and would be fine with a short MK day. If that would have been true with the rest of my family, I really and truly would have definitely picked a non party day for our past trip.
From previous experiences when we got to the park right at 4 for a party, our experience was that between 4 and 6 p.m. with both sets of people on those party days I can attest that it really is a mod scene.