That doesn't disprove Jibber's point. The "crappy and no real diesel" jeep is still an American car and since it has a plastic cover, your original point fails.
I understand that English is not your native language, but did you not read my post FFS? I don't care whether they make a difference or not, my point was that they are ugly; not that they provide less dust or whatever the hell you are talking about.
I disagree about them protecting the engine bay against Dirt and Dust. They may look nice at first, as there nice smooth surfaces, easy to clean, but take off the covers and have a look underneath. It will be covered in dirt and crap, just like any other engine bay over time. I disagree about them reducing noise too. I've driven a multitude of car's without the engine covers when road testing them after they have had some work done on them (there's no point in putting them back on until after the road test, due to something possibly being wrong), and i can confidently say i have noticed no difference whatsoever in the noise levels compared to when the covers were on.