You would have to cancel your H&V res. I chose the dessert party over Minnie's Holiday Dine around the same time last year.. unfortunately no earlier times were available.
The dessert party was totally worth it!! I've read the same sentiments from people on this site who also attended the party. Go for it!
If you read the threads/trip reports from people who attended last year, they all appeared to enjoy it. Most of the haters watched it on YouTube and decided that it was horrible.lol
Check out this thread-
http://forums.wdwmagic.com/threads/jingle-bell-jingle-bam.929782/
Welcome
.People just like to pounce. Got under my skin too, then realized that it just wasn't worth it, you'll learn to ignore it. Makes it a much better experience! Typically the trip planning and trip report sections here are full of great information and advice!