What is the strategic gain from hacking NYT? Identify potential other sources (within china) perhaps?
Even their public outing is good for them. The fact that this story is out there will make it less likely that Chinese dissidents will dare talk to NY Times reporters. Which means that dissidents will have a harder time getting their stories out to the world.
There are other benefits to the Chinese as well. For instance the rich data that the Times has about various US organizations could help them identify people who could become useful informants.
More often than not, the journalist or their editor get tips from people in the know (who are trusted NOT to disclose that information to you). Only then does a journalist start combing public records to have a verifiable (and non incriminating) source -- there's just too much to look at without some initial hints.
Perhaps they are looking for information about the tipsters.
And the sad thing, it is not limited to bureaucracies or government organisations. I have seen bugs that are not fixed, patches that are rejected because it allows someone somewhere to behave heroically in an attempt to impress someone.
When I first experienced this, it was a very real WTF moment from the School of Dilbert Mismanagement.
---email---
Hey [NYT reporter,] you may wanna check this ....lists wealth and place where this can be verified...
James ---------
--------- email 2
Hey NYT Exec got a tip from a State Dept source regarding Chinese leaders wealth.... --------
Maybe they'll get a "I can't believe he/she gave me herpes" email or at worst they mess with, and raise the cost of doing business for NYT. The cost to the Chinese is as close to zero as possible, they have the money and manpower, so why not do it.