My personal impression is that hash rate is dictated by price and (more importantly?) technology, with rate reacting to price and not the inverse. The two big ramps were directly related to a paradigm shift in mining tech, CPU to GPU, and GPU to ASIC. With ASIC gear becoming increasingly efficient we will probably see a rise in hashrate even in the face of a flat or modestly declining price. The upcoming halving should be pretty interesting for those watching this relationship.
It's not inconceivable that hashrate actually drives price in certain scenarios, once you consider the possibility of mining operations hedging by entering into futures contracts, and potentially establishing a floor based on buying instead of mining to satisfy those contracts at certain price levels.