I'd stay away from K&N. There's a reason they flow more then stock filters is they don't filter.
In 02 I bought a Suzuki Grand Vitara with the v6, stuck in a K&N and thought all was happy until I decided to clean it one day and found a thin film of dust inside the intact tract. Threw it in the trash and put the stock filter back in.
This coming from a guy who has three motorcycles, two quads, dune buggy and a diesel truck. Most of my riding is in the desert so I know about dust. I use stock filters for all my vehicles and have no troubles.
Don't waste your money. If you want performance lose twenty pounds.
SP
I think you may have just had a bad experience with that. My current car (99 BMW M3) came with a K&N cold air intake on it, and I drive 100 miles day in pretty dusty area, in the 2yrs I've had the car I've put 46,000 miles on it. My point is I've cleaned my filter twice (cause it was black instead of the freshly oiled red color) and I've never had anything on the inside of my tube, no dust, nothing.
I've used the drop-ins in past cars (08 BMW M3, 05 Ford Mustang) as well and never had any problems with them letting in unwanted particles. And with them all you definitely notice a difference right away, sometimes can hear it.
The cleaning is pretty easy though I am WAY overly cautious with them, I usually plan not to drive the car for day when I clean them. I spray them with the special cleaner, hose them out really well, repeat if needed, then let them dry all day. Then the next day I spray on the oil and let it dry for about an hour or two (says 20mins), THEN I finally put them in the car and drive. My current car I only cleaned it so much cause I drive a LOT and in pretty dusty area so it does get a lot dirty a lot faster than normal. Also it's a cone so it's more exposed to outside dusty/debris.
I highly recommend them, and if I get a Sonic I will definitely be looking to get one as the first thing I do.