For our first trip in 1996, DH used the touring plans in the UG to come up with a version for our family. It was pretty close to the actual plan in the book. Since it was Dec 27-Jan 2 - the BUSIEST time of the year, and we were travelling with a 7 week old, a 4 y.o. and a 7 y.o., it was perfect! We saw EVERYTHING and didn't spend more than 15 minutes in line for the whole trip. (stayed off site, too)
Since then, we've gone at quieter times. Usually, DH will create a plan for us that's pretty close to the UG plan, but we'll modify as we go along, especially if the crowds, etc are light. I always advise anyone I know to use the plans if they go, or at least use them as a base for their own plan. The "arrive early" mantra is something that people really need to get their heads around, and in my mind that's the most important part of the plans. The next important part would be understanding the rides and attractions and how they operate, load/unload, etc.
But, inevitably, people I know don't use the plans, ignore most of what the book suggests, and come home saying, "Ok, it wasn't bad, but I wouldn't go again in a hurry. Too much money for too much standing in line." I think one of the reasons we go back again and again is that we get SO much from the trip, without breaking the bank, and using the plans is what's made that possible for us.