Yeah, I wouldn't count 051 in the total numbers. So I would say somewhere between 17-19 either modern or somewhat modern destroyers.
2 052D as 2nd one is about to be ready and commissioned, and there are another 5 or 6 in various levels of construction. At least another 2 will be ready sometime during 2015, but I am not counting them in here, so lets say 2 for the year of 2014.
6 052C
2 051C
2 052B
1 051B
2 052
4 Sovremenny (2 of them more upgraded)
Total of 19 destroyers, but PLAN has almost 20 054A frigates, so that's a modern force that is also worth mentioning, and cannot be ignored. There are also another 2 "standard" 054 frigates, total number 22 by the beginning of next year, as 20th 054A has been launched a month ago already and will soon be commissioned.
So I am not counting old 051, or any other older frigates such as 053 and other various upgrades of this class.
I am also not counting 056 corvettes, even though they are new and modern. I am also not counting 022 missile boats, that are stealthy and China has 83 of them, and they do pack a LOT of missiles though. They shouldn't be ignored as they are fast and small plattforms that pack together massive number of anti-ship missiles, and could operate in those areas within the First Island Chain if needed.
Regarding modern SSK, China has 38 - I am counting only modern ones (Improved Kilos, Song & Yuan-class), Japan has total of 16 SSK (11 Oyashio and 5 Soryu) I haven't counted PLAN's SSNs here.
Not to mention that PLAAF har about 2,5 times more modern fighters than Japan has. Then you have H-6K bomber to launch another massive pack of missiles without problems from the Chinese mainland in addition to all other land-based missile systems on the mainland.
Regarding Japanese destroyers, I would say they have as of now 24 either modern or somewhat modern destroyers or frigates.
4 Kongos, 2 Atago, 4 Akizuki, 5 Takanami, and 9 Murasame where at least 5 Murasames are already from the 1990s and somewhat old / somewhat modern.
If you take away 4 Sovs of PLAN and 2 052 then PLAN has 13. If you take out all Murasame, Japan has 15.
From now on and towards 2020 and beyond, there is no doubt who has the power and building technology to start building serious number of destroyers. As you mentioned, there will be 12 052D and 055 is going to be layed down already next year while Japan will build 1 Atago and spend 5 years to build one.
So by 2018 when all 12 052Ds are ready and couple of 055 too, then China is already by that time above the very modern numbers of destroyers compared to Japan.
In the meantime, PLAN will be pumping out 5,000 tonne stealthy frigates also of course, which will be successor to those 20-22 modern 054/054A now. So by 2018, most likely add another 8-10 frigates to already existing number.
Then even more SSNs and SSKs of course. And missiles in general, and even more fighters, etc etc.
Basically, the crazier the Abe is, the larger military spending will China have, and that's a numbers game Japan is definitely going to lose big time. As mentioned, he is the "best" reason for increased military spending. He just keeps giving "gifts"
May he be "prime minister" forever