You know I bet only a quarter of the North Korean army vehicles actually work, the other 3/4 being used for spare parts to the keep the first quarter going.
South Korea is one of the largest economies in the world, well fed too. I bet they would walk over NK if it came to that....Provided China didn't get involved.
My guess is the Chinese view NK as not a problem until it becomes a problem. In other words they won't invest military resources into NK unless it is purely in their own self interests to do so...my guess.