I had my last car (a Renault) done with the official treatment, G3 Glasscoat, same sort of stuff as the one Mercedes offers. Cost me £300! I am a disabled driver (Motability) and this seemed a good idea at the time to keep it looking good.
A couple of months later I took it down to southern Spain and back.
It was very noticeable all the bug splats on the hot bodywork, and they were there for life too, well engrained into the paint finish. I gave it a couple of washes during the trip to remove the bugs and the dust using those spray wands. When I got back and had it washed properly the whole of the front was damaged and the wing mirrors etc. covered in splats. I took it back to the dealer to complain, and their cleaning bloke took it round the back for a while. It was maybe 50% better, but it never really recovered.
Then later that summer the other half went to a garden centre and bought a lot of pots of stuff. As the boot was full of sacks of compost, the plant pots, wrapped in newspaper, ended up on the back seat. Some water must have leaked because the seat was damp. A quick wipe down and it all looked good again until the winter and freezing temperatures overnight. The two of the rear seats now have very noticeable white marks. I suspect that the treatment (G3 Glasscoat) has lifted on whatever leathery stuff Renault put on the seats.
I'm not greatly concerned - I have a new 2012 B Class (W245), with most of the toys, coming in 2 -3 weeks and I will be glad to get rid of that Renault. A total rattle trap...
Meanwhile my warning to you is do NOT apply any coatings of any sort. Use the traditional cleaning and waxing techniques as detailed on other pages of this Forum.
P.