I was trying for that Arizona (Monument Valley?) look too, but the texturing was a bear. Without a lot of vegetation to break things up, it's really difficult to make a bunch of sand look like anything but a bunch of sand.
First area gets around that problem just by having a lot of junk in it:

Lots of little tufts of grass, scattering of trees, and an eroded out landscape to break everything up. Even that wasn't enough, though, just look at the layer-cake texture job I had to do on the right: 100% stone, then 50/50 stone/dirt, 100% red dirt, and then highlights of white sand. It actually looks like a mess in default light; it's only with some harsh overlighting in-game that it blends together.
This is the best picture I have posted of the less verdant desert areas:

You can see in the center-right how I tried to break it up with a little bit of dried mud, 1/0 brush at 100% squiggled around. If you download the module (Danaan v200) you can poke around in the Wadi-al-Khanal area and see some more open desert. I guess the main trick is just to make something interesting in the background, out in the unwalkable area, to draw the player's attention so they don't spend too much time looking at the ground. That and always try to have some sort of feature that you're drawing on the ground, like a hillock, dune, or gulley, instead of just leaving bare dirt. Like have a big splotch of darker sand, edged with lighter sand, and then highlighted with lighter sand in the middle.