Hi Melissa!
My whole family, including my dad and step-mom, dressed as pirates for the
Pirates IN the Caribbean Night on the Disney Magic last July. We all had a great time, especially my 5 year old, at dinner. However, when it came time for the party itself, my wife took my youngest back to the stateroom and the rest of us went up to Decks 9 and 10 to enjoy the party.
It was fun and a unique experience, but I have no regrets that my youngest child missed it I was expecting something like a Disney stage show, but the show on Deck 9 was more like a "dance party". The coolest part was seeing the Disney characters dressed as pirates, but you didn't have to go to the party to see Mickey and Minnie as pirates. You could see them much earlier below and have your picture taken with each.
The fireworks were nice, but more like what I would typically see at a local 4th of July fireworks display than something I'm used to seeing at a Disney theme park. In other words, it was nice but not spectacular. My family is going on another Disney cruise next year, and the only thing I would do differently is I would take my youngest to the stateroom and insist my wife go and enjoy the party with our oldest son.
Enjoy planning and have a magical vacation!