Bill, unless you have some abnormal nostalgic obsession with Route 66 (like my daughter does)don't plan your trip around following the route. For instance, don't drive miles out of your way to see the Blue Whale. Include 66, of course, to find specific remnants that interest you, but don't miss worthy attractions because of adhering steadfastly to the old trail. In other words, just plan a nice trip across the center of the nation. You'll see some nice country and meet some fine people.
My family and I have traveled probably three-fourths of the route. My daughter has chunks of old asphalt, splinters and paint chips from various famous landmarks along the way. We've spent the night in the "teepee" motel, and we've sweated out the night in some musty old motels that in their day provided nice accommodations. It's easy to get caught up in the history and the legacy of the thing (Buzz and Todd and their blue Corvette actually inspired me and my bud to give the experience a try. Finding a job/adventure in every little town you come to is not as easy as Buzz and Todd made it appear; they never ran out of money and had to come home.)
Again, don't make this a Route 66 trip. As others have said, 66 in most cases now lies under a modern new highway or interstate. The remnant motels, diners and souvenir shops in many cases are almost invisible, having been surrounded by new modern businesses.