RE: K&N Filter
I'm running a K&N filter in my '90 Westy.
As a test, half way through a 3,000+ mile trip (and right after a full
tuneup) I swapped in the K&N filter and Bosch Quad Point plugs.  The I
checked the mileage very carefully.  As I had expected, no improvement
in mileage, nothing, nada.  I've been running the K&N for three years
now, clean it every six months or so and especially after running in
heavy dust conditions, seems to work fine.  I will probably need to
run it another few years to break even on costs vs. a stock filter.
BTW, the Bosch Quad Point plugs have not been pulled in 13,000 plus
miles but no problems.  I'll pull and check them before the next long
trip or when I need a tuneup.