We celebrated our 7th anniversary on the Magic two years ago. We booked a res for Palo, and they brought out a sumptious chocolate cake, in addition to the three desserts we ordered. (I was 5 months pregnant and very hungry!) It was a great way to celebrate, and I'm glad we did Palo instead of our regular dinner rotation that night.
I also noticed that there are packages that can be purchased for $30--they decorate your door, hang banners, and more. I found that on the disneycruise.com website.