As someone who was born in Hong Kong and have lived there for quite a while, I'd say hong-kong.cn is definitely worth way much more than its registration fee, especially when all other TLDs are gone. However, a couple of things come into way: a) the hyphen hurts; and b) local market in Hong Kong is REALLY bad there.
For now, I don't think you will be able to sell it for even the low hundreds; but if you can hold on to it for say a year or two, it could go for a lot more.
The fact that you do have some Hong Kong/Chinese connection adds to your advantage.
Disclaimer: I'm not a big fan of .cn and have yet to register my first.