In our experience the parties have never made sense for what we want out of Disney, but there are a few scenarios where they might make sense for you and your group.
1. You are only going to WDW for 1 or 2 days or just an evening. At this point, you are spending close to the same price as a 1 day ticket and are getting some extra perks
2. You are in a group that prefers to visit late at night rather than in the morning
3. The exclusive holiday offerings are your primary reason for visiting (things like exclusive characters, holiday fireworks/ parades, going in costume, or snow on main street
If it seems overpriced to you don't do it. you won't enjoy it while thinking about all the money you spent.
For my family, there is plenty of Christmas and holiday cheer during regular park hours for us and we usually have trips that last 4-5 days so adding an additional day to our park ticket is much cheaper. We also have small children who go to bed early and wake up early so, we prefer early morning hours.
I also second the comment about the close to Christmas touring. If you go any time from DEC 23rd to 31st, MK is basically a free
MVMCP. Its SUPER SUPER crowded, but awesome. The best part is they open a lot of those days at 7AM... so if you wake up early enough you can do tons of stuff before the crowds descend. They also run the Christmas parade and the Christmas Fireworks.