"There's a thesis (whose most notable proponent I know is Peter Thiel, though this is not exactly how Thiel phrases it) that real, material technological change has been dying."

Tyler Cowen is again relevant here with his http://www.amazon.com/The-Great-Stagnation-Low-Hanging-ebook/dp/B004H0M8QS , though I think he considers it less cultural than Thiel does.

"We only get the Hansonian scenario if AI is broadly, steadily going past IQ 70, 80, 90, etc., making an increasingly large portion of the population fully obsolete in the sense that there is literally no job anywhere on Earth for them to do instead of nothing, because for every task they could do there is an AI algorithm or robot which does it more cheaply."

As someone working in special-purpose software rather than general-purpose AI, I think you drastically overestimate the difficulty of outcompeting humans in significant portions of low-wage jobs.

"The concrete illustration I often use is that a superintelligence asks itself what the fastest possible route is to increasing its real-world power, and...just moves atoms around into whatever molecular structures or large-scale structures it wants....The human species would end up disassembled for spare atoms"

I also think you overestimate the ease of fooming. Computers are already helping us design themselves (see http://www.qwantz.com/index.php?comic=2406), and even a 300 IQ AI will be starting from the human knowledge base and competing with microbes for chemical energy at the nano scale and humans for energy at the macro scale. I think that a 300-IQ AI dropped on earth today would take five years to dominate scientific output.