Bob, here's my take on it: you are correct, the PCV valve was originally intended as an emissions control device, but it had two unintended beneficial consequences...by pulling much of the blowby out of the crankcase it prevented the buildup of acids and other contaminants in the motor
oil, promoting longer engine life; it also solved the oily mess around the breather or the road draft tube that older, non-PCV motors typically have...even engines in very good condition have some blowby, so most of the guys here would do it just for the "tidy" factor, and the better engine health is a major reason to put one on for a street vehicle.