I was shocked you said there isn't anything in Winslow. You missed the museum, the historic trading post that is now the visitor center, the historic La Posada, the outdoor railroad cars, the 9/11 memorial park with 2 of the largest pieces of the twin towers and my favorite vintage hotel along route 66, Earl's Route 66 Motor Court. I stay there every chance I get.
Just by watching it I can tell all of these places are worth to be visited, although, personally, I'll be most interested from the Petrified Forest and the petroglyphs as of course from the Grand Canyon. Greta trip! 👍