We went to the MVMCP on December 8th this past year, and found it was well worth the money if you maximize your time. We aimed for getting there for 4 pm (you can get in as early as 4 with your party ticket), but got there closer to 5. In those 7 hours, we rode Buzz Lightyear, Space Mountain, Carousel of Progress, TTA, Splash Mountain, Big Thunder Mountain, Haunted Mansion, Teacups, Pooh, PhilharMagic, Peter Pan, & Small World, all with little or no wait. We also ate dinner at Pinocchio's, stopped once for cookies & cocoa, met Scrooge McDuck, and watched Holiday Wishes then stayed to hold our spot for the 10:30 parade. If you plan to stay for the whole party, ride as many rides as you can while the first parade is happening and wait for the second (less crowded) parade like we did, I think the party is totally worth the money.
We were a group of 6 adults, so there are bedtimes to consider if you have young kids that might not make it until the end of the party. Also, since they did away with the Twas the Night show, we weren't interested in waiting to see the new Stitch stage show, so we focused on rides, the parade, and the fireworks. Also, we were staying offsite, so attending EMH for low crowds/wait times was not an option. If you only want to ride rides with no wait and are staying onsite, you'd be better off doing the EMH for free rather than spending $55/person on party tickets.