The only thing I see, is that unfortunately you're not going to have a lot of time to spend wherever you are. You're going to see a lot of great things on the road, however I would definitely consider sacrificing a couple of places, to have an extra day or two elsewhere. You'll be surprised how easily you won't want to leave a lot of places. Not only that, but you're going to come across SO many amazing places on the way, you'll be gutted you can't stop at them all because of your tight deadlines.
Let me give you an example, seeing as you mentioned Flagstaff.
Me and a buddy decided one weekend to drive from LA to Phoenix, just for something different, came across a bunch of really cool little towns on the way, but unfortunately passed through as we were on a tight deadline. We got to Phoenix and looked around, realized that there really wasn't much there after catching a baseball game. As neither of us had been to the Grand Canyon, one quick look on the iPhone showed it was only another 5 hour drive away, so we decided to drive there too. On the way, we drove through flagstaff as it was the way the map took us, and we saw a bar so thought we would stop to freshen up. Both of us ended up falling in love with the place and people instantly, we decided to spend the next few days there, staying above the bar. After talking with a few locals over a couple of nights, they told us about this cool little spot near a place just south called Sedona. So we drove to Sedona. Which was a great little spot. Driving back to Flagstaff to finally head to the Gran Canyon, we heard of another little spot called Slide Rock.
http://www.google.com/imgres?q=slid...rt=19&ndsp=21&ved=1t:429,r:4,s:19&tx=59&ty=87
Literally a water slide carved in between the rocks by the water, where everyone just goes and has a great time, as its usually unbearably hot. A load of fun!
So anyway, moral of the story. What was supposed to be a weekend away, turned into a week and a half vacation, where we saw way much more than we ever thought we would, and found out about a lot of cool spots we would never have heard about, if we didn't stop in Flagstaff and love the place so much.
If you don't allow yourself the chance to stop, take it in and be spontaneous, you risk missing so much more than just another stop from your itinerary.