Car dealers/service people like to push new air filters. I take my vehicles in for oil changes (we can argue why some other time) and the first hint of dirt in an air filter, they want to change them. I always thought that air filters were more effective once they got some dirt in them. I often argue against it, but then get the run-around about engine damage, poor fuel milage, etc. Obviously, I wouldn't allow them to get as bad as off-road engine filters running in dusty conditions, but I tend to think they are just trying to bleed a few more bucks out of people.

What is the consensus here?