when I visited Death Valley, it was hott and there were no clouds.
despite all that, your shots are simply stunning - not sure what else you are took and it would be awesome to see more.
yes, time is of essence in that area, since there are so many spots to "drive to" and shoot from and there is no wrong or right, its all based on just luck - which you seem to have.
The weekend I was there was actually quite crazy. The clouds and the full moon made for very nice opportunities and I was able to take some advantage of that.
Unfortunately the winds were scary. It was not just the tents and skirts that where flying. Get careless for a sec and the camera and the tripods would fly off too. The entire trip we had to deal with 60 to 70 mile an hr winds. Copious amounts of sand and dust everywhere including the camera.
Had the shot composed and then would have to wait 10 to 20 mins for the winds to subside a little bit to get the shot. I dont think I was every this scared for my setup.
The Tokina 11-16mm is a great lens but left me wanting occasionally for a longer focal length. I'm seriously considering the Nikon 10-24 and 12-24 but, but, I just might return to the Tokina 11-16mm.