First, on the sand, the calcium sand is far worse than regular play sand, for two reasons. 1, they add calcium carbonate to the sand. The other place calcium carbonate is added to sand? The concrete industry, because it helps the sand bind and clump when wet. 2. Because it has the calcium carbonate in it, it is more likely the dragon will try to eat it. That stuff is pure bad news.
The greens thing isn't horrible. I like to mix mine up, but as long as it's a good healthy food (mustard greens, collard greens, turnip greens, dandelion greens, etc...) And add some variety, I don't think you'll have many problems. I never have. I use mustard greens as the base of my daily salad, as they seem to go over the best, and buy something else to mix in sometimes (other greens, escarole, endive, etc...) Some grated or minced butternut squash, a little mango or papaya a few times a week, etc... Variety is definitely good, but it's not bad to use the same thing for a week or two and then switch, I'd just avoid feeding nothing but one thing only.