I think the value of the trick or treating depends on your child. My son is not a big candy kid, so he did one or two spots (IASW was particularly cute) but didn't get caught up in it. I saw some kids running around from spot to spot, waiting in long lines for a handful of candy, and then running to the next spot, and I thought, "what a waste of time, they could be riding rides with no lines". Then I reconsidered and thought, "Boy do they look like they're having fun!". It's also how I feel about autographs sometimes, until I remind myself how much fun it is for the children to collect them. For the most part they were older, and probably staying until midnight, so had plenty of time to ride rides, and probably can't trick or treat at home any more due to the coolness factor.
With a 4yo I would recommend getting there at 4, because if you wait until 7, I think you'll feel rushed to get things in before he crashes and won't get the full advantage of the rides. We went at 4, still avoided WTP and Peter Pan due to lines, fast passes were already closed down. At 4, people who have been there all day are trying to get last rides in before the park closes at 6, so it's pretty crowded. We spent our time on the TTA, Teacups, Carrousel, anything without a line.
We think it was a great value and would do it again. When the party started my sons rode at least 15-20 rides, and those most popular in their age group. My 4yo went on Goofy's Barnstormer 5 times in a row, one time without getting out of the plane.
