Unless any of the shows are must-dos for your family--some are really fun to see, I doubt it's worth that much money for you because you are budgeting.
Rarely appearing characters are fun, but the lines to meet them form fast and can be loooonnng. Who wants to hang around for 30-45 minutes or more to meet a character when you've only a few pretty pricey hours for partying?
Here's something that might help you decide if the party is worth the cost to you--watching 4K WDW's video of an older one:
4K WDW films have no narration and are done from a person walking about's viewpoint, ambient sounds only. You get a good sense of the actual experience, I think, from these videos.
I can really understand your wanting to say the hey with it and laying out the bucks for the party. We didn't stay till the end either time but still thought the cost worth it for the holiday atmosphere. Even though you know it's not real, watching the snow fall along Main Street after dark is sooooo Christmas card-like. Just lovely.
Okay, I'm doing a rotten job of arguing my earlier probably-not-worth-it. Given that this may be your last trip, doing the party might be for you. Good luck

deciding and have a magical

time whatever you do.