I would agree on most of your points except I wouldn't use the adjective "dumb".  Most people are going to look at it from their own point of view.  Maybe we could state that our opinions pertain to our present location rather than making generalizations.  The majority of would-be miners don't have the knowledge to use server power supplies and break-out boards and import duties, taxes and electricity costs are regional.
 I would argue your final point however.  Friedcat has essentially declared economic war and intends to unleash cheap and numerous miners onto the market to pare down the competition.  I don't think 15% or more sustained diff increase is unreasonable.  The summer was an anomaly it should be discarded from your diff estimations (IMHO).