Both Bltizo and I believe it is the PLA is reviving an old tradition of secrecy, as mentioned above. At the same time, according Dr. Larry Caldwell (retired) of Occidental College, one of the reasons why the USSR remain so secret about its military capabilities was to hide its own weakness, so NATO would act with prudence after overestimating Moscow's military strength. Not sure if the PLA is doing same, but we do know that both the 052Cs and 052Ds are inferior to Aegis destroyers in terms of firepower and range (though not necessarily electronics).
Um, I never said anything about the Chinese military "reviving" anything... what I said is that they have relatively high opsec. What I mean by this is that they are more secretive compared to the military of most other nations. I never said that they are becoming "more secretive" compared to previous years or that they are reviving an "old tradition" -- they've always had high operational security, and like tphuang said, they are actually far less secretive now than they were before.
In China's case, after observation from recent years I think their secrecy is about hoping their enemy underestimates their capabilities and developments rather than overestimating it. For instance, if the US knew how many 052D destroyers China was going to build, or how many carriers China was planning and when, or how many fighters or AEW&C the air force needed, that would allow the US to develop and plan for counters accordingly.
I use the J-20 as an example -- if China had been as open about J-20's development as the US was about F-22, then the world would have known about it as early as 2000 most likely, and that could have driven the US to produce more F-22s or maybe permanently station more of them in the western pacific, or develop counter stealth radars faster, etc.
In other words, by maintaining very high operational security, the Chinese military manages to deprive the opposing side of useful intelligence that they could use to develop counter weapons and strategies for. That means the opfor will need to expend efforts to try and identify what the actual capabilities of the chinese military are (why else do you think the US is constantly wanting China to be more transparent about its military capabilities).
But secrecy can also be coupled with misinformation. countries like Iran or North Korea are also secretive in their military developments but more often than not, they also display military projects which are fantasy, or very early in development, for the sake of nationalism and as a "warning" to the US. obviously such "warnings" are laughed out of the door.
However in China's case, military projects are kept very secret until they are in advanced development -- and the more potentially useful they are, the longer they are kept in the dark. I suspect this is so that if a conflict ever does break out, the Chinese military will have a larger number of weapons that the opposing side is not expecting to be fielded and are unprepared for, which can help even the playing field for the PLA a little if they are facing an advanced and large opposing force.