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.
Agreed. Hashrate should follow price, but it seems like during those two massive increases it was the price chasing the hashrate....
Someone better suited to scientific analysis of data sets would do a better job of analyzing this relationship ( hint, hint, Professor Stolfi ) 
Anyways, I don't expect any further large expansions in mining technology or efficiency, certainly nothing on the scale of cpu>gpu>asic.
Many people mocked me many pages ago for my concern that the block size could not simply scale exponentially for the next 20 years, but I still believe we are reaching the limits of physics and any further significant exponential type gains in computing power beyond asic will likely take us beyond the singularity. I just hope our new synthetic overlords accept bitcoin. (Ok, yes, I've been watching too much humans (tv show))
