As to whether or not the touring guides are really necessary probably depends a lot on the time of year a person is going. I've only been to WDW once in the summer and that was the middle to end of August, so I don't normally go when the crowds are real large.
The first trip or two we followed the touring guides for the most part. After that, we knew the things we wanted to do, the things we wanted to skip, and the new rides that we wanted to try. The last trip (I had only my 4yo with me and we met my sister) we knew what rides to go to first to avoid long waits. We hit them first and then were very flexible. Again, this was during a slow time, the beginning of February, so we could wing it for the most part. We like to repeat our favorite rides (Tower of Terror, Test Track, Splash Mt, Big Thunder, etc) so we needed to get to some of them early and we used fastpass whenever possible.
I think for a first visit the guides are especially helpful to follow. I now use them as more of a planning resource, and they are very helpful.
T&B