@Liam ********
easy with the "I don't have to do it until I get back" line of thinking. IF you have time definitely GO and get the stamps moved.
You might get grief at the airport for NOT doing it seeing as you're supposed to move extensions/re-entry permits to a new passport BEFORE you exit the country. It's only people on valid multi-entry visas <- (which you are not on) that carry both passports.