As an electrical engineer with 20+ years professional experience with automotive electrical systems, I will say that there are threads of truth of in what you posted...but also many misconceptions.
While electrical connections do corrode in time, most modern vehicle electrical systems use the chassis ground
only for power circuits like the lighting and starting systems. The sensors as you described (temperature, flow and pressure) are 2-wire devices, and do not use the chassis ground as a reference (analog common). This is done to address many of the potential problems you mentioned, plus a few others like electromagnetic interference ("noise").
By the way, dissimilar material are very prone to corrosion in electrical circuits. Mechanical connections mating copper, to gold, to sheet metal would, in time, also show oxidation at the mating surfaces. Automotive connectors use a tin-lead plating on contacts for general purpose circuits, and silver or gold plating for more sensitive or critical systems (like airbags).
By the way, I stated "Most automotive alternators are in the 65-75 amp range", so there was no correction required. Most cars on the road ARE Civics, as you mentioned, so it sounds like you and I are in agreement here.
What is the point of the statement about "alternator strain" and turning on your headlights, etc??? The alternator load translating into a HP loss to the engines net power to the crankshaft - and improving the chassis ground will not reduce the amount of load the alternator placing on the engine.
I hope this helps.