I took mine off .. I got sick of worrying about them all the time, mine got yellow patches on them from bird droppings etc even though I cleaned it off straight away, I used to wax them as well but it still didn't help much.
I think the factory stripes are of a pretty cheap quality, when I took them off I was quite surprised just how thin they are.
Also they cost over A$300 (150 pounds) to get a new set over here from Ford as they would need replacing fairly regularly, on top of which .. who puts the new set on? .. will they put them on straight? etc .. I just couldn't be bothered with it all anymore ... off they came!