It depends--some of the tours are offered a couple times a day, every day, while others are only offered a couple times a week. Usually I've found that if I call the first day or two of a week-long trip, then I can usually get something for the end of the trip, but I go in off-season.
My favorite is the Segway World tour--I've done it about 4 times or so with various family members. It's my Mom's favorite too.
I did the Yuletide Fantasy tour and was a little underwhelmed. I thought we would get more information on the specific significance of the decorations at each place, instead of the more general holiday information we got. Plus, there was a lot of times where they had discussions like "what holiday movies do people watch?"
I also did the Backstage Magic tour and although I thought a lot of the places we saw backstage were interesting, I would have enjoyed going backstage at the attractions more. We only got to see one attraction, and then were taken places like Human Resources. It may have been that a lot of the people on the tour were sort of grumpy as well, that made it a little less "magical." It was ok, but at the price, I wouldn't do it again.