The UG website keeps the best days updated and the touring plans are not contigent upon being there on the best day -- they work beautifully. However, those who wish to "wing it", throw the touring plans out the window and wait in line are welcome to do so.
As for me and my house, we're going to take advantage of the UG's touring plan recommendations and enjoy a wonderful and relativelly wait-free day in the parks. After two visits to WDW and a visit to DL they haven't steered me wrong yet.