I swear a good aftermarket airfilter is all you need. Unless you do regular off road driving in tons of dust. Visualize an old air filter. How much dirt and trash does it have on it? Not that much usually.
I believe in air filters, and have changed filters regularly, that is twice a year, on a couple of old Volvos we drive plus on our 240D.
But - for what it's worth - we also have a 71 GMC three quarter ton pickup, and 17 years ago we put a rebuilt motor in this vehicle, and I'm embarrassed to say the old air cleaner assembly didn't fit the new rebuilt motor, so I left it off. It was my daily driver for eight or nine years, several miles every day on unpaved roads. I still use it to haul firewood. The motor is in pretty good shape.
So I'm just saying that air filters are important but I wouldn't make a religion out of them.
Marketeers probably look closely at air filters and think of ways to hype them because they are easy do it yourself items.
Harvey