[mwebb]

"Something else that has occurred to me; somewhere I learned an older car (ie more than 100k miles on it, or 5+years old) tends to experience some corrosion and degredation of wires which puts more strain on the electrical system.

The solution was to put in a larger battery to ease out the extra strain, ie adding a capacitor would also help."

no ,
that is NOT the solution and adding a capacitor will not help either.

the solution is to do voltage drop testing , ie measure voltage lost across a given wire UNDER LOAD using a DVOM - negative test lead on the most negative side positive test lead on the most positive side

if you screw up and reverse the test leads ,
it does not matter , the value will be negative , just reverse the test leads and retest
or just use the negative amplitude value .

the value must be under 50mv for a smart circuit like a circuit with sensors in it or
under 100mv for a dumb circuit like a circuit with computer operated actuators ie injectors , solenoids , relays , etc
or
under 200mv for supply or starting circuits
like alternators and heater blowers and cooling fans and starters

if you find higher than specified voltage drop , locate and replace the bad component which means replace the connector or solder on new eyelets or replace the cable or what ever it takes to
get voltage drop back to specification
=========================
never use an ohm meter for this
unless you enjoy chasing your own tail with out ever catching it.