I think you might be thinking of MNSSHP's parade (Boo To You), which is pretty elaborate and a full parade. MHP (at DL) has the Calvacade, which is like a mini-parade. It's cute, I haven't heard of too many folks that say it's better than Boo To You. The fireworks, on the other hand, are arguable better at MHP. Both Screams (MHP) and HalloWishes (MNSSP) are great, but I like Screams because it has Zero!
If you hop over the HalloweenTime SuperThread you'll find a FAQ for MHP on Post #3. It includes a link to comparison between MHP and MNSSHP.
http://www.disboards.com/showthread.php?t=3270919
Yes and no. The rides (HMH and SMGG) run all day, so they are not party exclusive. There is also the Big Thunder Ranch Jamboree/Carnival, which operates during the day. There are Halloween decorations (mainly on Main Street and a little in Frontierland and NOS), but a lot more are added for the party. You'll see some of them starting to come up before the party (basically being set-up), but not all of the effects appear pre-party.
Sorry, no. Trick-or-treating only occurs during MHP.