In my opinon, the Western Express route is primarily intended for people who don't have the time to do the whole TransAm. If you have the time, I'd recommend the regular TransAm route.
I think Pete has a typo in his first bullet when he said what direction he thought the winds favored. But maybe I'm wrong. Pete?
The must-sees are different for different people. Some people would consider Disneyland a must-see, but I doubt that applies to most touring cyclists. Most touring cyclists just want to soak it all in and might find a particular tree or cow to be a must see, or talking to a particular local. Some would consider as must-sees the Cookie Lady in Rockfish Gap, Danger Hill in Christiansburg, pie at Cookie's in Golden City, the Dragon Lady outside Summersville, the springs at Alley Springs, Yodeling Katy in Chanute, Hoosier Pass, Grand Teton, Yellowstone, ACA headquarters in Missoula, fireworks on the fourth of July in Lander, the Oregon coast, the Twin Bridges bicycle campground, the Prariie Chicken capital of the world in Cassoday, Dusty Gilmore in Ash Grove, Schechter's hostel outside Guffy, Mammoth Cave, Gillian Hoggard in Ordway, etc. Simple stuff.
How long will it take? It can be done in as little as six weeks or as many as sixteen. The longer you take, the more memorable your trip will be.