YAY FOR YOU!!! 
Just finishing a cruise myself I am now back to being the jealous one! Palo is definitely a great experience, and I will make a recommendation there. Dinners on the boat are already fabulous and where lunch is good, it tends to be similar most days except maybe the day before you return to port where they, at least on the 6 day, had a great seafood buffet luncheon. I say go for the brunch so as to be able to have a great Palo experience, but at the same time, not take away from any of your nightly experiences with the dining room, especially since on a 4 night, you only repeat 1 dining room, but it still has a different menu! Also, schedule it on a day at sea so as not to interfere with a port excursion.
Don't wait to book it when you get on ship. We booked it several weeks out on line when we did our advance check in paperwork. By the way, make sure to do that as soon as you can so you can get a good boarding time for the ship. They'll give you a boarding time and group number. Show up a good hour before that time. You can get checked in and beat the rush before they call your boarding number. Remember to practice your pageant wave for when they announce you onto the ship then make a beeline for the buffet! Oh, and make sure to pack a couple bottles of alcohol in your carry on as Disney allows that! 
We snagged a drink of the day in the souvenir cup then used it to mix our drinks in. 
If you haven't already, while booking a stateroom, check the layout of the ship and try to make sure you aren't above or below an area that may tend to be noisy such as a night club or a kid zone.
Where are you sailing to? Got any excursions lined up? Do tell! I am now living vicariously through all you who have vacation plans as I start to look ahead to summer 2014! 
