If China wants cheaper resources, it need only prop up the U.S. Dollar less (i.e. hold down the Yuan less).
China has large foreign currency reserves. It can buy what it wants. An ill-thought invasion merely reduces the amount of goods that China could sell to the U.S. and EU...which would cause job losses and wage declines in a China that is already under social pressure...hardly the recipe for a tasty oriental dish.
...but then people with that kind of power and ambitions (and irrespective of what folks want to believe, the PRC is still a totalitarian state) have never been known to make rational decisions.
They are rapidly building their military, they are blustering and threatening their neighbors and ourselves, and they may at some point feel the "need" to galvanize their public behind such action. What they consider historical ties and even "ownership" to places like Taiwan and Siberia could easily fuel it.