Thanks. I was afraid the post would sound a little arrogant.
Basically, when I first adopted the uro, I thought that her husbandry needs were basically the same as my bearded dragon but with slightly higher temps and little to no insect matter. I contacted Robyn from pro exotics and he basically asurred me that they are two very different animals that require different care. He also pointed out in a way that I was sort of thinking about my needs more than the reptiles' needs, so I decided to do some research, and substrate is by far the hardest decision to make I think. You can go one of two ways:
1. Naturalistic. It looks nice, it makes the animals feel at home, but it's a pain in the a** to keep clean. Basically soil is the most naturalistic substrate, but I see two downsides to it. First, the vermiculite could cause some problems if an animal accidently ingests it, though Robyn located some very nice soil for pro exotics and he doesn't have to worry about the. Second, like I said, pain to keep clean. If you have a huge enclosure I wouldn't worry about it, but with what's considered "normal" sized enclosures, you'd have to do some pretty diligent work to keep bacteria from spreading through the tank from a couple of wet leavings.
2. "Sterile". Not exactly, but that's sort of a good way to think about it. Substrates that are easy to keep clean, like paper. But the downsides to these are a lack of natural stimulation and, as stated, lack of gripable surface. I would also consider millet to be in this category, even though you do need to do a little more to keep it clean. These substrates are also the ones deemed "safe" to use, where there is little to no chance of impaction.
Robyn has made great steps forward in the naturalistic sector of substrates, but I think maybe we should also try to step forward in the sterile substrates category. Millet is great, but I think if we tried we could find something even better. I know over at the bearded dragon forum they have been doing a lot to try to find the "perfect substrate", and for bearded dragons, a lot of the small time breeders over there think they have found it in "non adhesive rubber shelf liner". I have yet to try the stuff out, but it seems great. It easily wipes clean and you can switch sheets of it out once a week to clean them thouroughly. It also is grippy enough that the bearded dragons can get good traction on it, somewhat like walking on hard, packed soil of their native land, but a lot less messy. Because of their slightly more watery feces, this stuff probably wouldn't work well for uromastyx, but you get the idea.
There's a lot more research to be done on all this stuff, so I think I'll have a pretty busy summer this year. By the way, have you every used a "nest box" for your uros? Just basically a rubbermaid shoe box filled with soil and sand, with a flexy tube coming out the side for entrance? I'm thinking of trying one of these, but I haven't heard much about them.