I have changed the stock paper airfilter along with the sparkplugs in my E36 BMW 325i once since I bought it with 140k on the clock. It now has 308,000 miles on it and still runs awesome using very little oil. Watercooled P-cars... pretty much the same situation. The only way I would bother with changing road going airfilters more often is if I drove them off road in dusty conditions often.
The tiny foam airfilter on my airplane gets changed once a year at annual inspection time even though I rarely fly it enough hours in a year to need it.
My MX race bikes got a freshly cleaned and oiled foam filter every race, as it would be covered in dirt..... My street driven cars.... not so much.
