I'm going to give serious thought to the cabin filter, as I typically own cars 10+ years and thought would seem to pay off. I've used K&N air filters on all of my cars, but after reading a few posts on this forum about dirt being allowed in, I'm not so sure.
The air filter is usually the least restrictive part of the intake. The biggest restiction is nearly always the convoluted trunking before the air box. I would now only use a K&N if still doing serious enough off-roading that could lead to water getting into your air box, wet paper, not good.
Also depends on the areas that you live in - temperatures, type of dirt, size of particles, etc. An oiled-gauze type air filter may be good enough to stop the majority of the contaminants that it shouldn't affect lifespan of the vehicle that much. Like they say - your mileage may vary.
K&N setup is good enough for TRD to use them as the vendor for TRD badged performance air filters (looks exactly like a K&M filter, just different colors).
I've been running a K&N on my 2002 Corolla once the powertrain warranty ran out (60K miles) - have little over 205K miles on it, with 145K of those miles on a K&N filter. Pull UOA (used oil analysis) annually to check on the condition of the car - as I run extended oil changes. Both wear levels and amount of silicon contamination (usually a sign of sucking in more dirt) - were pretty much the same between running the OEM paper vs the K&N aftermarket.
Much of the issues I've notice on the boards on running these K&N is likely due to improper oiling techniques to re-establish that oil "tack" behavior. I clean my K&N once a year (remove, wash, dry, re-oil, replace) and re-oil every 6-months. There is a trick to making sure that all the pleats get the right amount of oil.
I only like them because I can run one filter for basically the life of the car. Cost and performance wise - they are pretty much the same. What you save in number of paper air filters - you'll eat up with maintenance on the cotton gauze one. K&N is not as acoustically "quiet" as paper - so you'll hear more of the intake noise compared to the OEM one, but MPG, acceleration - butt-dyno said no difference.