The only time that you would even think of replacing con rods is if they were mechanicly damaged in some way, like a spun bearing in the rod [fixable] or it's badly bent [hydraulic lock?] or failed a crack test.

Some of the fastest engines around have been remanufactured using servicable but definately ""used" con rods as these are probably the toughest part of an infernal conbustion engine, Well,... in a Datsun they are.