The rest was irrelevant due to the point I singled out. Mining with CPUs wasn't a problem until GPUs came online - and since they were so much more effective that caused a disruptive shift where all CPU based mining stopped. The same will happen in the shift from GPU to ASIC.
I agree with you that GPU mining will eventually be made unprofitable as ASIC mining (and botnets) takes over, but that has to do with difficulty adjustments, not price adjustments. Difficulty is a lagging indicator of both price and technology available (ie; difficulty will tend to reach an equilibrium where mining with whatever technology is available is slightly profitable - which is why mining is a "race to the bottom"). However, barring cartel action by miners, price doesn't really reflect whatever technology is being used to mine bitcoins. You could blow up all the ASICs and GPUS in the world tomorrow and mining difficulty would still try to adjust to where mining was just barely profitable for most operators at whatever the current price was.