I currently own an '04 Grand Prix GTP Comp Edition with crome wheels. As described by 07 MKX, the cromed aluminum wheels are very suseptable to corrosion. I have to get the wheels re-sealed every 4 months because of corrosion. It sucks. For better or worse, I bought a warranty on my tires from a shop (even though I didn't buy the tires from them). They re-seal my tires at no additional charge each time now. I think I got lucky, I don't think they should be doing that for me. If it were my business, I would not offer that warranty.
I anticipate that the crome plastic covers are going to be easier and cheaper to replace than chromed aluminum wheels. I could use some more info on those wheels too. Any chance any of the Edge owners want to post some pics with the crome plastic wheel cover pulled off?
I will not get chomed aluminum wheels again. I cannot tell if the wheel is plastic or metal unless I knock on it anyway.