I live in Arizona too, up in the White Mountains. I think dry, hard pens are your friend because it keeps the feet hard and dry. I keep my guys barefoot and use Easyboot Epics in the rocks, but most of the time we ride completely barefoot around home.
Like was mentioned before, we can only guess as to what is going on, but I would think if there are multiple cracks going on, the feet are too long or improperly balanced. Sometimes cracks are chronic and it is hard to get rid of them, especially if they are due to a defect in the coronet band of the hoof. But it sounds like if your horse is springing cracks right and left, the hoof is long and maybe imbalanced.
So, everyone has a different idea of what they want to do, but I personally would go back to barefoot and just boot in the rocks. I only have to boot the fronts on my guys.
The feet to have to be kept trimmed and the edges rasped to keep them tidy when going barefoot for you will get chips. But small chips have never caused me a problem. It is just nature's way of trimming long feet. If I start getting chips, I know it is time to trim/rasp.
PS. Re-reading your post, I think I know what you are talking about. I think you are having problems with quarter cracks and that can be from contracted feet. Larger shoes with room for expansion are the way to go if you are keeping her shod. That, and I bet the farrier is relieving the quarters where the cracks are. My friend had a horse that was the same way. The crack actually started from the top down, not the bottom up. Personally, I still think barefoot is better for contracted feet, but I don't want to start a barefoot vs. shod debate. Those never go well!
I don't use any external hoof products on my horses, (unless they get thrush), so I don't think the lack of moisture is the problem. Moisture comes from the inside out. I think if they are getting a healthy diet, you really don't need feed-through hoof supplements either. But they can't hurt I suppose. My horses have really good feet on just an alfalfa/grass mix diet.