My Smart gets substantial OFF-ROAD miles and I have to change it every 6k-8k depending upon the frequency I drive home down the very dusty dirt road I live on.
That being said, I bought a car in the 90's for $100. A VERY NICE Toyota Tercel 4WD wagon. Owner said he took it to a mechanic and it was diagnosed with a bad distributor. I offered to look at it for him and he said he was taking it to the junkyard so we came to the $100 deal AND I pay him whenever as he didn't care. In a rush I looked at it quickly, turned it over and could tell it was getting fire but wouldn't start. I pulled the air cleaner lid with the air filter to see if it was getting fuel. Turned it over and it popped right off. Flipped air cleaner lid over and looked at filter and it was a mess. Spent $50 on a tune up and it ran perfect for 2 more years. Sold it for $2700 after that.
Just checked my Smart's air filter before I headed down to Orlando and it was nasty. Lucky I keep a spare in the garage so I was able to swap it. (of course I can "CAN" it off my other Smart) (( "CAN" - military aviation term meaning to steal the part off of a good airplane to fix a broken one))