Until recently people haven't tended to use digital cameras for KAP, partly because of price and partly because of shutter speed. Even with suspension rigs cameras do tend to bounce around a bit. I have seen a few recent articles with digital being used. The "cheap-ass" digital cameras are the one's least likely to be suited to KAP, unfortunately. I have a couple, and they both have fairly low resolution and require a lot of light.
As to flying height, the low lengths of stunt kites make for fairly boring shots, at least when you take a whole role of them. Higher shots are good, but at some point you have a hard time seeing the camera!
Some of my pics. More to come in about a week.
"No, no, I don't mind being called the smartest man in the world. I just wish it wasn't this one." -- Adrian Veidt/Ozymandias, WATCHMEN