Let me pipe up as another male voice on this subject. Many people have already said that there is no easy way to define "Disney Magic" but what they have ended up communicating was the experience they had. The one thing that you find in common with all their experiences is that WDW touches you in a lot of ways deep down that makes it hard to explain.
Some of the more common "Magical" experiences that I will echo are:
-Coming through the Gates under the Train Station and seeing Cinderella's Castle for the first time-I been down there 7 times and it gets me every time.
-Watching your kids interact with Mickey or any of the other Characters.
-Being greeted by Cast Members at any of the on Property Resorts with "Welcome Home"
-Hearing the otherworldly/Futuristic music as you walk through the Gates of Epcot and move towards Spaceship Earth.
-Watching the Wishes Fireworks shows in the Magic Kingdom on Main Street in front of the castle with your family.
-Seeing my DS11 face when he came off Rocking Roller Coaster for the 1st time at Hollywood Studio's.
-Listening to my DS9 Laugh/Scream as we went down the Red Slide together on a 2 person inner tube at Blizzard Beach.
Some unique "Magical" experience that we had are:
-My whole family was escorted to a special private viewing area at Epcot to Watch Illuminations just because I had struck up a random conversation with a Cast Member!
-On our Honeymoon Found Champagne waiting in our room when we first got there along with a note congratulating my wife and I-Found out that was not standard that was thrown in just because we had told them at the front desk it was our Honeymoon.
-Off Duty Cast Member walked me from downtown Disney Bus stop to hotel I needed to get to in order to pick up a rental car.
-Got to participate in the show at the Monsters Inc Laugh Floor as "That Guy" my kids were cracking up!

-Got to ride in the front car of the Monorail with the operator again just because I struck up a conversation with one of the Cast Members on the Platform.
My wife and I realized last time we went that the Magic is not just the rides, the shows, the fireworks, the Hotels, the music or the Cast Members it was also something we could actively participate in even if only in a small way. We decided to make a conscious effort to be Magical where we could. We took pictures for families where the Dad or Mom were taking pictures of the rest of the family. We struck up conversations with other families on the bus back to the resort asking them what there favorite ride was or where they were going tomorrow. This often had the effect of distracting the little ones from their tiredness as well as reminding them of what they had to look forward to. We ate lunch with a very Kind elderly couple from Belgium who offered to share there table with us so we could sit down at a very busy restaurant in Epcot and in doing so I saw them smile more then a few times as our boys shared there excitment over there last ride. We also realized as we did these things that we went deeper into the "Magic" ourselves!
So I guess all I can say is enjoy your trip and i wish I was going down sooner.