Wow so many replies, I'll address some older ones.
An example of being bogged down in spats are the Diaoyu Islands and Arunachal Pradesh claims. If we're being real here, these disputes are not going to be resolved any time soon as long as the US is number 1. Can China beat India/Japan in a 1 on 1? Yes. But if you bring the US into the mix? Then no. China stands far more to gain through economic cooperation with both than to press claims that are just not going to happen. China as it stands is currently still only the 2nd strongest power. Wouldn't it be smarter to focus all your energy on taking down the number 1 and keeping as many countries neutral as possible. For this new Cold War, China cannot face another NATO as the USSR did. The West and US allies in the East are disunited and squabbling between each other (see South Korea/Japan spat). They are mostly economically dominated by China but don't think for a second they won't sacrifice that to join the US. Overall, China has won nothing in diplomatic disputes except to confirm to the other side why China poses a threat. China has to keep US allies neutral so it has to lay low and maintain the status quo until it can topple the US.
China is growing at a rapid rate both militarily and economically. However, it is still weaker than the US in pretty much every regard right now. Why pick a fight now? Why play a game with a weak hand when a couple rounds later, you will have a much stronger hand? Mao's approach to border disputes was to simply push it off until China got stronger and could force the issue. China's greatest advantage is the fact that is has long term thinking and strategies. Kissinger once said that US strategy is like Chess where they aim to get a quick checkmate through a power move to instantly end the game where as the Chinese strategy is like Weiqi. It slowly builds up assets through a long game until the lead is insurmountable. Currently picking fights seems like trying to get a quick checkmate and resolving the issues rather than quietly building strength until the enemies see the writing on the wall and back off. Win without fighting. It's a classic Chinese strategy that has been played without fail.