Okay, I'm going to take a shot at these fenders. I have had my element for two weeks and it has been darn cold so I've only washed it once. As I said, it has been cold and my fenders seem fine, although I have not hit them with a hammer. The fender material seems to be the same as the early years of the nissan frontier and I have seen a number without scratches or cracks. I have the Y model, (EX) and the finish is different the the dx. I am not anticipating any problems. Most cars and trucks on the road are mostly plastic and I think cracking is rare. If there is problems with these fenders, it will probably show up in canada first, as I said, it is darn cold. I'm not sure what the fuss is about the fenders. I had plastic fender flares on my dakota and they held up fine.
I am sure that this did not answer any of your questions, but I like to hear myself type. If you not comfortable with the fenders, wait a year and see what happens. Or talk to someone with a frontier, the new ones are still plastic, just color coded.