Just keep it. It will go forever unless Asiana changes its rule again. With 16k, 3 one-way Korean domestic flights, or 1 Korea-China/Japan one-way ticket you can get, or you can give to your family. It might be helpful if you happen to visit Asia, and to make cheap routine. Who knows how Asiana will change in better way, so just keep them.

Or when you fly Asiana, you can purchase inflight duty-free items using miles, with more or less 10 USD/2000 mile ratio, with very limited selections. Or you can book selected hotels, in worldwide. There are many many more options - movie theater or online shopping mall, etc - but exclusively for those living in Korea. Unfortunately, all these information are only available in Korean language. dang!