I have the same problem on a 2009 +4. First noticed at about 6,000 miles. I took the doors off and took the hinge pins out. There was noticeable wear on one side of the pins so on installation rotated the pins 180 degrees and swapped top with the bottom pin. Also greased the pins well before installation. I am now at 10,000 miles and the wear is starting to show again. I haven’t taken the pins out again so I do not know if the pins have rotated back to the original position or I have more wear. The problem with replacing the pins with ones made of a harder material would be the hinges would wear not the softer pins and the pins are easy and hopefully cheap to replace. If you are going to take the doors off just make sure you protect the wing with some rag or suchlike just to stop the door from swinging back once you have removed the retaining strap. As others have said removing the doors is an easy job and with the hinges off the pins are easy to remove.
