So, I was going to originally suggest the Ultimate Thrills Tour but when I read that your wife wasn’t a thrill seeker I wasn’t sure if she would love it. But, that’s what we have booked for April. I think that would be a truly memorable day. Here is a review that I read. An 'Ultimate' Trip Report
Your family might like the After Hours event, but it’s pretty late (9pm-12am), so that wouldn’t be ideal for my family. I think it would make the next day a little rough. We’re better at getting up early and getting out rather than staying up late and sleeping in…though it does look cool to see Animal Kingdom at night.
Also, I suggested the CRT fireworks party since you said your wife likes princesses more than DD!
There are several options for boat rental as well. There are pontoon boats, which are the least expensive…but if I were going to splurge I would get a larger sized boat that might have a bathroom on it to be more comfortable for the duration of the cruise. Then, you could cater a bottle of champagne, desserts, etc.