I've never used K&N filter lube stuff.
Just a quick spray over with any thin oil spray.
you can get way to anal with all this stuff.
I had a really nice special foam air filter that I purchased for my Acura, made by a racing shop in Southern California. Discussion boards said that in my model the filter unleashes an unusual amount of horsepower. I noticed the difference right away.
I figured the same way, any thick oil should do, why spend more for genuine filter oil? Oil is oil. I had a bottle of STP on the shelf already, and I figured that it would be perfect since it was a nice thick viscosity. It completely ruined the filter....and now those special filters are out of production so I can't replace it.
I know that a K&N is of a different construction, but how often does it need to be cleaned and oiled? Every couple of years? And a can of K&N filter oil is only about $5 and easily available. It might be worth the extra couple of dollars to go with what the manufacturer recommends in this case.
Bear in mind most cars run fine for years and years with the same old cheap dirty air filter in, you'll sell yer bike in a few years time with hardly any miles on it anyway.
I wouldn't leave a really dirty air filter in my bike, or car, for "years and years." Air filters are cheap enough, and easy to change. Changing out a dirty air filter usually makes a noticable difference is gas mileage, if nothing else. I'd prefer to have the few extra horsepower and MPG a clean filter provides.
Just another view.