Just to clarify. Prism is separate from the Verizon data dump. We're talking access to information that Google, Facebook, and other internet giants can track about you. Including emails.
China is demonstrably interested in this. When they broke into Google's network, they went straight for the private emails of Chinese dissidents. (With, apparently, much less success than they would like.) When they broke into the NY Times, they went looking for any information about dissidents that the NY times might have.
From the sounds of it, access to PRISM gives them that, all nicely gift wrapped and correlated with other signals of interest, tools to locate known associates, etc.
Why are they interested in this? The Chinese leadership apparently do not see a war with the USA as their top risk. (Though they do prepare for the possibility.) That is because they know that the USA is not in the habit of lightly invading nuclear powers which could easily level multiple US cities in retaliation. But overthrow by revolution is something they are terrified of, with good cause.
One of the things that's probably in PRISM is a list of people who are currently suspected of being Chinese agents. That's very important information if you're China.
China's also known for doing indirect attacks, where they try to compromise one system in order to get clues on how to compromise another. Having access to PRISM, depending on how it's implemented, would potentially open up access to all sorts of information collected by American tech companies. Heck, if they had access to social-graph data, they could determine who is friends with a lot of employees of the targeted company, and that would be a likely person to try to mine for trade secrets.
I wouldn't rule it out. According to the reports from early this year, China appears to be very interested in finding sources and dissidents, which is why US journalists have been hacked.
No it wouldn't. You'd be after the things Chinese spies are already after: trade and military secrets. They don't care who's calling who.