I have done two tours at Walt Disney World. Both have been absolutely worth it.
My favorite tour I have done is by far the Wild Africa Trek. It was a great way to get up close with some animals, and you learn a lot more than you would if you just go on the safari. The only difficult part is the rope bridges. The planks you step on are sometimes a lot further apart than you might think. They designed it to look like they are "old" rope bridge. They do have rope right below and you are tied to a cable above, so it is safe. It still freaked me out having to sometimes step what felt like a yard to a little more just to reach another plank. It is also not guaranteed to see every animal. I went close to the end of the morning/afternoon, and we did not see the lions. This tour is worth the price, and I will definitely do it again.
The other tour I have done has been the Steam Train Tour at the Magic Kingdom (This tour might not be offered when you are there due to the upcoming refurbishment of the railroad. I'm not sure when the refurbishment ends). This was also a fabulous tour and one I would do again. If you plan it for a day that doesn't have extra magic hours at the Magic Kingdom, we got into the park about 15 minutes before it opened, and we got some really great photos of Main Street with no one on it (This could change since the Welcome Show is now at the castle instead of at the train station). You then go back to where they keep the trains, and you get to go inside the locomotive. Afterwards, you travel back to the Main Street Train Station where they talk about the history of the Walt Disney World Railroad and Walt Disney's love for trains.