I change the stuff that matters (e.g., fluids, plugs and points back in the old days of leaded fuel) early, but the stuff that doesn't really matter (e.g., PCV valve, air filters, wheel bearing grease ... ) only when needed, which in some cases is never. At 600k miles, my Mazda still had its original PCV and the original grease in most of its wheel bearings. I had to replace the fuel filter only once.