I would suggest not getting into the mindset of "why this, when I do that" because you'll just go crazy. (just ask Capn') These CIS-E Jetronic fuel systems are pretty complex for their time, and as DOC stated, there are multiple sensors that relay information to the control unit.
The microswitch, although it may appear still good, may be worn out, in the sense that it takes the little arm more travel to activate the switch. I recently had idle problems and replaced mine (was $23 at dealer) and all idle problems are gone.
As far as the high aux fan problem, check the 2 pole blue temp sensor on the engine head, right side, just forward of the single pole engine temp sensor -- for a loose connection. This is an open resistance switch, so if the connection is taken off, the fans will automatically turn on high.