Williams is a definite stopover and about an hour to walk the route 66 shops.
The grandcanyon is about 100 miles round trip from Williams. There's a Harvey house there, El Tovar. Memorable well served higher end restaurant. It's the best place to park, walk around, eat, museum and shop.
Food in Williams is not worth eating anywhere except Jeff's at Goldies. It's an old original Dennys from the early 60's and the food is the legendary route 66 fare. Edible, distinct, immemorable, it's every diner you've seen in every 50's movie about travelling. It could have fell right out of EasyRider(yes, I know that's not the 50's)
Through the canyon on az64 past the little grandcanyon(I like it a lot and it's a 30 minute stop) up toward 4 corners. Don't bother with four corners unless an 8 year old just has to go. It sucks. Others say differently, others have to say good things because of the abysmal drive they made to get there instead of researching and passing it up.
If you instead Stay on the 40, Winslow is a place where the poverty will make you weep, but a restored Harvey house is there along the railroad tracks. Excellent restaurant with at least 1star Michelin food.
While still in California there is a restored Harvey house on Kelbaker road. Look up the ghost town its in, Kelso, and the dunes. It's worth a 90 minute side trip.
Get off the 40 at ludlow. Make a right. Take the 8 minutes to drive through what's left of a vital 1880's through 1940's Town.
The loop the other direction on Kelbaker leads you on an old part of 66 that loops back up to the 40 at mountain spring. It's like something out of Road Warrior(the first madmax).
Look up 'two guns' it's a ghost town ish place right on the 40. Its a must stop if you have 30 minutes. It's right on a ramp, no travel away from the freeway. It's a defunct tourist trap from the 50's through 70's.
Gallup got nothin' keep driving.
If you're adventure driven a drive through the Navajo rez to canyon de chelle, lukachukai, and over the pass into new Mexico is a trip you'll talk about every chance you get.
If you're lucky the swap meet in Shiprock(look up Shiprock) will be open and the Navajo food is worth the experiment. It's ugly, but just walk in like you're a local and you'll find them very welcoming.
These aren't in order of any miles or importance. They're just places we enjoy that popped into my head, where an rv can easily travel(both the head and the road).
There are 100's more, but without knowing your interests or path it is a waste to list them all.
We've spent two weeks on the stretch stretch from needles to ludlow and have another week planned, but we need a month. We could spend a year between Barstow and Gallup. There is a lot to see and do.
I think you'll find Santa Fe a bit anticlimactic. The culture and shops are painted with one, narrow, uninventive brush. Taos the same.
(if you're going to Santa Fe because of the art, pm me. I have some Penni Anne Cross ORIGINAL paintings for sale or trade. Value means nothing to me in a trade. Make it interesting is all I ask)