You are absolutely correct about K&N filters being worthless. Worse, they lead to increased engine wear.
I have done a lot of dyno testing on Jaguar V8 engines, both supercharged and naturally aspirated, in conjunction with my avocation of developing performance parts--exhaust and intake systems for these cars.
Some of the tests involved comparing power output with standard OEM, Fram and Purolater air filters with K&N filters and no filter at all. There was no difference in power output between any of the options. Of course, these were all new filters. It is possible to show a difference when comparing a very dirty filter to a new one.
The owner of the dyno shop performing the tests told me he had done dozens of similar tests for other customers and in only one or two instances did the K&N produce additional (negligible) power. Those instances were on very large displacement truck engines and may not have had new, clean OEM type filters for the baseline tests.
Furthermore, the Jags we did use K&Ns on for up to 10K miles showed significantly increased levels of silicon (dirt) and wear metals in the oil analyses we did at 5K and 10K miles.
Not only do these filters not deliver on their hype to produce more power over regular cellulose air filters, they pass so much more dirt into the engine that wear rapidly increases soon after their installation.
I suppose their claim to additional power could be somewhat valid as the increased wear opens up the tolerances in the engine which results in less friction and thus more power. But, while this may be effective in a race engine with a very limited life cycle, it seems like an expensive way to get slightly more power from normal service engine.
Both Fram and Purolater make excellent automotive air filters. Stay away from the Fram oil filters, though. Again, based upon testing and examination of their design, construction and filter media, the Frams are pretty inferior. Purolater does make excellent oil filters. We've found others that are good as well, but these are the most widely available.