I went on the Keys to the Kingdom tour last year. I found it very interesting and a must for any Disney Fanatic.
Keys - $45, 5-hours - must be 16 or older; admission
Magic - $199, 7-hours - must be 16 or older; no admission
Details of tour;
Learn about the names in the Main Street Windows and how imagineers make Main Street USA look bigger and longer.
Tour of the Utildors (underground maintenance/Cast Member access system. Its basically the guts of Magic Kingdom.)
Tour the costume dept.
View the backstage area (behind PoC, Splash Mountain, etc.) check out workshop for parades (where all floats are located).
Learn about a ride (we did Haunted Mansion) and ride it with no wait.
Learn the requirements for being a cast member (hair lenght, fingernail lenght, # of piercings, etc.)
Stop for lunch...
If I remember correctly, the tour was from 8 am to 1 pm (or 9 to 2)
That's all I can remember right now. If you are looking to learn more about Magic Kingdom and don't want to spend that much, definitely do Keys to the Kingdom. If you want to learn more about all parks and price isn't a concern, then I would go for the Backstage Magic