Most serious printers that I know use the dichromate contrast control method for reasons of consistancy and workflow. It is described in Dick's book somewhere, unless he took it out of the 2nd edition.
For the same reason, most serious printers will replenish their developer faster than minimally necessary. If you plan to make a print or two now and again, using old developer will work fine, as Sandy does it. If you want to be serious about pt/pd printing and desire the predictability and consistancy to make high quality prints efficiently, you will probably come around to a point where you are not using heavily aged PO.