Its my understanding that a round wire recoil spring might chew up a plastic guide rod. I have a CZ aluminum guide rod with a Wolff spring on my P-01 for that reason. That could of course be all hearsay and rumor, and I expect the experienced gunsmiths like schmeky to know more than I.
Outside of that possibility, the polymer guide rod is fine and the only reason to replace it is if you dislike a heavy wallet.