As a Chinese domainer with 8 years domaining experience, as well as a NNNNNN.coms player since earlier 2014, I am also totally confused in the NNNNNN.coms bulble...
I do think there are certain value for some kinds of NNNNNN.coms such as ****88.com, which are used for Chinese targeting casino sites. However, average $600 for a ****88.com is definitely another gambling of investment.
I picked about 150 pieces of ****88.coms on April 2014 at average price of $50... Then sold all of them around $100 - $250 price range when the bubble comes from this Aug end. The price are jumping to $500 = $600 after my sold out... But I don't regret to my decision because of I don't know what will happend in next month...