My 92 Civic has very old spark plug wires, probably original, but their resistance is in-spec (under 20k ohms), they have no external damage, and the vehicle has no misfire or other symptoms associated with bad wires, aside from having worse gas mileage than it used to. Is there any reason to replace them? Would doing so perhaps get a more optimal spark timing or stronger spark, more-complete combustion, etc.? Or are those claims just made up to sell wires?