We are an every-3-year family, too - we just went over President's Day and our last trip was February 2015. Things that were new for us:
EPCOT:
Soarin Over the World at EPCOT. Same ride platform, but we really got a kick out of the new film.
Frozen Ever After (we rope dropped this one). Great fun.
Mission Space, Green Side. The mission on the green side has changed and now orbits the earth. The orange side still goes to Mars.
We happened to be there for the last day of the art festival and that was neat, we loved the mural painting and other activities.
Animal Kingdom:
Pandora!!! We loved it. We managed to ride Flight of Passage three times in our trip. Absolutely amazing ride. We skipped the new boat ride.
There are currently lots of new babies in the park. We saw the one month old new baby hippo with his mama, the tiger cubs, and the baby elephant.
There will be the new Flights of Wonder show when you go (both Nemo and Flights of Wonder were closed when we went).
Hollywood Studios:
Star Tours - new movie with scenes from the Last Jedi in the simulator. That was fun.
Star Wars Launch Bay - we didn't do this but there are character meet and greets in there.
Galaxy Far, Far Away show. Cute and we had a good time watching it.
March of the First Order. Fun to watch.
And obviously Toy Story Land will be open for you when you go. A little jealous. LOL!
Magic Kingdom was largely the same and we really had bad luck when we went over President's Day week (we were there on Thursday and EVERY headliner was down at some point in the day - Thunder Mountain, Mine Train, and Splash Mountain were down all day, Space went down in the evening). Frustrating, but also just unlucky. THe rides (except Space) were all functioning the next day. There is the new Muppets show in Liberty Square that is very cute. We loved that.
