As diesels are basically big air pumps, would a wee bit of an improvement be had by going to an oil-soaked air cleaner such as an Amsoil or K&N item? I have also thought that perhaps some improvement can be had by using one of those air cleaner lid things with filter elements in the top (I do not know what K&N calls that product). I have read posts here that argue pro & con for oiled filters vs. stock paper elements. Even if a stock paper air filter flows as much air as an aftermarket Amsoil/K&N item, would not the aftermarket item offer better filtration of particulates?

Personally, I do not want to "Soup Up" my diesel - the car is saving my drivers licence; however I do want to make it as efficient as possible, in addition to enhancing its already excellent reliability & longevity.
Now, about those damn rotten switches & electrical glitches...