RE K&N filters
I agree, that putting a simple K&N filter into a mercedes will not achieve much, because of all the reasons listed above. However, I put a K&N filter in a 96 mustang (3.8 l, 6 cyl), and felt the following:
1) the lag in acceleration due to running AC is gone
2) Car surges forward above 3,500 rpm
3) slightly deeper tone under load
I know a couple of semi-professional rally drivers from NY running Subaru Imprezas WRX. THE FIRST thing they did was to throw out the factory air boxes and filters and replaced them with the injection air intakes with, you guessed it, K&N filters. Well, if the guys making a living (or some of it) while driving prefer K&N's, who am I to argue? As to the "more dirt" comment (the one about physics), it would make sense if the K&N filters were made of paper. But they arent. They made of cotton. The cotton is thicker than paper, so it has more surface area for dust particles to adhere . that's simple physics ! So, even though there is more space between cotton fibers, the thickness of material ensures you get clean air. Also, that means you can load more dirt (that's why you have to clean'em only every 40,000 miles).