Although the overall mining difficulty must go up, I think that in short term (say 4 - 5 days), the movement of mining volume / difficulty can share information about recent market sentiment.

I believe that miner is a mature participant in the market, thus their movement is somehow important to understand the market.

Actually I had plot a correlation graph and interestingly, the price (tomorrow) is quite correlated to mining volume (today).

So I will dig deeper in this area. Stay Tuned!