We specifically planned to come back the same week as the cast member party in 2019 after enjoying the same week in 2017. In 2017, we didn't have park hoppers and we didn't go to any parties and never saw fireworks (except during dinner at Cali Grill) but the light crowds on the day of the cast party made it all worth it. Our kids are meh about fireworks, so we didn't miss them. I walked over to MK after dinner at Cali Grill (and after the fireworks) and took a look at the castle lit up at night. (This was on a non-party night) The lines were way too long to get on any rides or even get any photos taken, but I got a good pic of the castle and did some christmas shopping. It was a great week. Am really hoping for the same light crowds on the CM party day as in 2017, hopefully those days aren't over!
PS. I got the 7:30 pm reservations at California Grill for 4 people the night before our dinner while checking the app around 10 pm.