Disney is ABSOLUTELY for adults!!!
I've been going regularly since I was 8 years old, so some of the rides I love as an adult and some I love for the nostalgia.
You are spot on when you mentioned doing the parks in the AM, breaking after lunch, then heading out after dinner. My grandparents got us on that regular Disney routine when I was a kid, and I still do it to this day.
I loved the other poster who said that as an adult, you notice the little details so much more. So true! You can really appreciate the creativity that goes into every single thing you see.
Some of my advice:
*Magic Kingdom is it's most magical at night. That's when the pixie dust is definitely in the air! I highly recommend evening EMH at MK - stick it out till most of the people have called it a night. It's so awesome!
*At MK, don't miss Splash Mountain, Space Mountain, Big Thunder Mountain, Haunted Mansion, and Pirates. I can't understand how anyone could not love Pirates?!?!? (From that other thread.) Jungle Cruise is all about the bad puns. With the right CM, it's hilarious. The other rides in MK are more nostalgia for me, and I don't always ride them, but they're still fun when I do.
*Dining (and drinking!) at Disney are part of the fun for us! Head to the Polynesian and get some Lapu Lapu's. Man, I love those! (Strong alchoholic drink served in a carved out pineapple.)
*Really take in all of World Showcase. (I love practicing my German with the German CM's!) Learn about the countries! Drink their wonderful beverages!
*Take your time walking through the jungle treks at Animal Kingdom. I LOVE animals, and I enjoy this so, so much. At Animal Kingdom, the rides to hit first are Expedition Everest, Kilimanjaro Safari, and Dinosaur. Then just relax!
*Overall, know that you will NOT see everything. Disney is huge! If you go in knowing that, you can relax more. Disney will still be there on your next trip! (You know you'll be back!

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*Don't miss Soarin'. It's great. When we took my parents and grandmother two years ago, my dad could not stop talking about it. He talked about it for a straight year after that trip...
*When people ask me what I love so much about Disney, I often tell them that I love it for two primary reasons:
My childhood nostalgia - I have so many wonderful memories from those childhood trips. My grandparents always let me help in the planning and it made me feel so special. When I'm on a ride in Magic Kingdom, for example, I really feel like I'm that little girl again, and all is right with the world. My grandfather's been passed away for 14 years now, but when I'm in Disney, I always feel like he's there with me.
I work in music/theatre/opera, etc. I so appreciate Disney's element of theatre - all around you at all times. You are completely immersed in a total experience during your whole trip. A ride is not just a ride - it has a storyline, and props, and scenery. Who else does that stuff?!?! You are no longer in the real world - you are in Disney!
Enjoy your trip. You will have such an amazing time! And you know we're all gonna want to hear about it when you get back!