Here are a few things you might want to be aware of:
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1) About four years ago, Downtown Disney doubled in size and became Disney Springs. It's gorgeous, beautifully themed, and has something for everyone. On a budget? Get your meal from a food truck and sit outside and listen to one of the bands. Splurge? Check out any of the gourmet restaurants. Lots of entertainment options too such as the Void, a balloon ride, amphicar ride (car that drives on land and turns into a boat in the water), bowling, moving statues... And of course shopping. You could definitely have a very special anniversary there. Our fam. even gave up a park day to spend the day at our pool and at Disney Springs. At the Springs, we spent happy hour at S-T-K Steakhouse (yummy small bites), experienced the Void, shopped, and enjoyed free live entertainment at one of the outdoor venues while we had our dinner from the 4 Rivers Cantina food truck. You can have a wonderful anniversary celebration whatever your budget!
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2) Disney After Hours was introduced in 2016 (I think) so this may be new to you. Specific dates are released just a couple or a few months in advance. Basically, for about the price of a theme park ticket, you can enjoy the park with very few people and almost no lines. I wrote about this extensively a couple of days ago under the "Disney Tips" forum, but in a nutshell, you have 3 hours in the park with very few people & almost no lines. CMs let you in the park 2-3 hours BEFORE DAH starts, so you have a total of 5-6 hours or maybe a bit more. DAH is offered for 3 parks - MK, AK, & HS - on specific dates this summer. Our family went to DAH in HS during Memorial Day week. No crowds, no blistering heat, got on and off all the main rides & saw several characters with little to no wait. Unlimited popcorn, sodas, Mickey Mouse ear ice cream bars, Mickey ice cream sandwiches, fruit bars (we consumed our fair share!). We did NOT do this as an add-on but did DAH instead of a park day. Spent the day at the pool, night at HS. Worked great. In fact, we loved it so much that we are planning another trip in August to do DAH at Magic Kingdom.
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3) THe Pandora area is new to AK. It is themed after the world of Avatar. Cool to walk through & especially lovely at night, as lots of items glow in the dark. Avatar Flight of Passage ride is amazing for anyone. The Na'vi River Passage is probably most exciting if you are into the movie. AK has some new restaurants in the last few years. Nomad Lounge is our fav for our budget - we enjoy the atmosphere and the small bites menu and find it to be a great oasis/watering hole when we're tired of walking ( you can sit at a couch & chairs indoors or out -- or sit at a table). Satu'li Canteen is the new restaurant in Pandora - fast casual & gets good reviews.
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4) Storybook Dining at Wilderness Lodge is the newest character meal. I haven't been yet but it gets great reviews for both the food and the character experience. Storybook dining is in the restaurant that used to be Artist Point. Characters are the Snow White, the evil queen, Dopey and Grumpy. I've seen photos and the place looks beautiful and very woodsy - seems perfect for Snow White. I nabbed a reservation at my 6 month out and am excited to be going in December!
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5) Toy Story Land opened at Hollywood Studios. My teenager loves it. Slinky Dog Dash roller coaster (easy one & cute) and Alien Swirling Saucers (cute but for littles mainly) are new; Toy Story Mania has been around but is part of the land. Cool theming. Usually can find a green army man, Buzz Lightyear, other characters standing around for character experiences.
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6) Star Wars Land at Hollywood Studio may be completely finished by March. Not sure. Galaxy's Edge, the first piece of Star Wars Land, is slated to open end of August. Millenium Falcon Smuggler's Run is the major ride; also you can build your own light saber, not sure what all else. Rise of the Resistance -- the rest of the land to be opened TBD, rumored to be sometime in the late fall. Many bloggers expect increased crowds esp in HS but in all lands due to the opening of Star Wars Land.
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7) I'm assuming that My Disney Experience, reserving 3 fastpasses at each park 2 months out, and magic bands were around when you visited 4 years ago? If not, I can post basics but you would want to research them and get on it well in advance of your trip --
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My family is calling so I guess I have to do something besides daydream about Disney today!

Hope you have the best trip ever and a wonderful anniversary! I'll post more if I think of anything else major that has changed in the last four years.