I read your post, and I immediately thought of two things:
A) For mass adoption, I would say that USD/MHs would have to improve. I know some people who would want to get into BTC, but don't have thousands or tens of thousands of USD to invest in hardware. Even a Jalapeno is barely in their budget. And the uncertainty that goes along with the current growth of the network, they can't stand not knowing when or even if they will get their money back.
B) The only way I could see power efficiency becoming important is if manufacturers started including Bitcoin hardware inside their equipment without informing their users. Could you imagine if every Dell or HP desktop tower had an ASIC built into the motherboard that mined whenever the computer was on? It wouldn't be much, but when Dell or HP get literally thousands of ASICs mining for them, it can add up. Lets say the chips were capable of a few GH/s, but used less than 1W. No user would every notice 1W increase in usage. An ASIC could be connected to any internet-ready device: switches, modems, routers, computers, cell phones, PlayStations or Xboxes, etc. The new PS4 and XB1 both have AMD APUs with a 8-core CPU and a beefy GPU. What if it was built into the firmware that they would mine LTC to a secret pool when you weren't playing a game?
K I'll take off my tin-foil-hat for now. Just some very tired ramblings.