I wish I had some "top secret" cool things to look for but everything I have, I originally found here. Still, in case others don't know -
MK
- Bow to Cinderella's fountain in FL - there's a crown on the mural behind her and when you bow (or if you're a kid) the crown just fits on her head
- Check out the mural as you go through the castle.
- In Frontierland look up at the second floor balconies. There's some great details!
- Find the "one of by land, two if by sea" window in LS
- Look up when you're shopping on Main Street. There's SO many little details inside and out.
- Same with FL - see if you can find Willy the Giant (from the short, The Brave Little Tailor)
- The streetmosphere CMs are the BEST. Keep your eye out for them and go out of your way to talk with them.
- The electrical water pageant on Bay Lake.
AK
- There's details everywhere you look, so these are just my faves
- Grad student drawings on the walls of ... oh, the eatery place in Dinoland. Whatever it's called. And the "in case of emergency" squirt guns there, too.
- There's a rickshaw you can sit in in Asia. Great photo op!
- Check out the yellow dino at the entrance to Chester's and Hester's and see if you can figure out what gender it is.
Nothing vulgar, just cute.
- The secret path between Asia and Africa. So peaceful!
Epcot
- There's a great inlay in the ground on the east (Land, Seas, Imagination) side of FW that's really worth seeing. Lots of quotes by famous inventors.
- The water play areas! I forget if there's two or three there.
- There's a gurgling water fountain along the backside of the coke building.
- Find the pickle tree in Germany!
- Belle's library in France
- Viking playground in Norway
DHS
- More streetmosphere actors!
- Lift the rug beside the line to Muppet Vision 4D
- I love looking up here too. There's so many great things above normal eyeline.
- See if you can find a package to "miss Dorothy Gale" over by IJSS.
Also, if you want to put increase your chance of getting surprise magic moments, it's simple. Don't rush. Get out of the main flow - if you're only on the paths from one attraction to the next you're unlikely to get tagged. Notice details - CMs love that! Let your child lead when possible and when you're not in a crowded situation (and don't rush them!) Stay positive, even if something goes wrong. Start conversations with CMs. Heck, just being nice to us makes our day! Don't expect anything but be open to whatever happens. Pass on the pixie dust when you can, whether through kind words to others, scooting over on the bench so they can sit, or giving them your extra FPs. Ask CMs if they have any favorites details or secrets to share.
And whatever you do, RELAX! Every. Single. One. of my magical moments was something I couldn't have planned for and happened when we had stepped away from the crowds for a moment just to enjoy where we were. You miss those moments if you treat WDW like a Six Flags, just a bunch of rides to see as quickly as possible.