Interesting discussion, just want to add my 2 cents.
It appears to me that China really has everything to gain and not much to loose here, the following being the reason:
1. China did not have a ADIZ before this while Japan, Taiwan, US and pretty much everyone else around it does. So really, by doing this it just kind of letting everyone know this is what I considered as my comfort zone and will watch anyone coming in so don't come too close. Also it marks the boundary where China feels it can effectively project its power militarily. Now whether it chooses to enforce this law is up to China, but now it can say it has warned everyone so no one can just go straight up to its border and claim ignorance as before.
2. Even if China don't want to mess with everyone coming into its zone or no one respect it now doesn't mean the situation will not change later. The zone will still there there. As time goes by and China increases its influence, others will know where not to tread if they want to remain on good term with China. Off course respect for ADIZ is all voluntary, but could carry economic and other consequences if not respected.
3. China's ADIZ by the way it is drawn neglects Japan's ADIZ over the disputed island so that put Japan and China on the same term. If japan throws a storm over China's intrusion into its ADIZ, China can claim the same for Japan.
4. The US move on China's ADIZ with the B52 may seem like a victory now, but it also lets China to do the same to the US ADIZ in the future. Even if China can't do this now to US, but keep in mind that China is developing its own carrier fleet. With the tech advancement, who says China wouldn't have a long range bomber fleet like US that could do so in the future?
The down side off course is that it gives other people leverage politically as we are all seeing today. But really, what does the Chinese leadership really lose here? They are not elected by the populous, and with Xi in control for the next 10 years he is not afraid of losing face in public. On the contrary, Obama is forced to pull off the B52 stunt because he is accountable to the public so even if the move is meaningless he has to do it so he wouldn't look weak and loose votes.
So really, China is the winner here in a long term game of strategy.