When we bought our 32-3 five years ago, the rope-to-wire halyards had been replaced with stronger, thinner all-rope halyards several years earlier, and we still had original sheaves. We did not see evidence of chafing on the halyards, even after several years (we substitute cheap messenger lines (box store nylon) for our main, jib, staysail, and port and starboard spinnaker halyards at haul out each fall, which allows for careful inspection and indoor storage of running rigging In the off season. However, we had significant (and embarrassing) squealing and squeaking when we raised the halyards, so last winter we pulled the mast and replaced all the sheaves with delrin from zephyrworks. The sails don’t go up more easily, but they sure come down fast!! And it is so much easier to manage our in-boom reef lines (we replaced those sheaves, too). And no more aluminum squealing. So, you probably don’t need to replace the sheaves when you switch to all-rope halyards (which you should definitely do), but new sheaves will be a nice upgrade when you get to it.