As mentioned, the trim is to make things look pretty. My XJ is an '88, so I'm going more for practicallity and usefulness, rather than looks. The pinch seam on the rain gutters are'nt an eye soar on my older XJ. The paint coverage was also decent, to where I was'nt concerned with rust.
Keep in mind I live in the desert, so rust is'nt a big concern. However if I had a newer model with nice paint, no dents or dings, I would want the gutter trim.