I've done both, Keys to the Kingdom about 3 years ago, Backstage Magic just this last January. While you see different things on both tours (except for the Utilidors which are on both), they are somewhat similar in the fact that you get to see the inner workings of the park(s). Keys is MUCH shorter, 3 hours, backstage is twice as long. Meals are included with both.
I would recommend the tours if you are interested in seeing how everything works, for us we love to see the mechanics of rides, attractions etc. If you are familiar with the show, How Things Work and like it, that's basically the jist behind these two tours.
I also wrote a VERY indepth coverage trip report of our Backstage Magic Tour which can be read here:
jeffreyjennifer.blogspot.com
Then Scroll down to Friday Jan 29th.
HOpe you enjoy the tour(s), for us they were absolutly worth the cost.
Jennifer