What's the difference of changing just the air filter (K&N), and changing/getting a K&N intake. power difference, and performance wise

 

This is a sound/appearance mod, not a power mod. The power difference, if any, isn't worth the cost of the system. The S filter is not a restriction for this motor. So a better flowing filter isn't buying you anything. Especially if that filter can let more damaging silicates into your motor. Use the stock filter. Personally I would recommend the stock filter, even if you do go with a K&N (or any other) intake. Mate stock filter to whatever intake you think looks/sounds the best.

There are mods you can do to your stock airbox for more sound, if that is all you want.

 

if your main concern is "sound". have you done the stock air box mod ? either way i would suggest using any filter you'd like but keep the existing plumbing factory for hot/heated air concerns.

 

I don't recall which ones have had issues but I seem to recall others inadvertently getting water ingested by the engine as the design of the air filter allowed water to be sucked in. Not good.

 

You're thinking of the intakes that place filter down low, behind bottom of bumper. If you drive through any standing water, and filter becomes submerged, engine will suck water and hydrolock. Blow holes in pistons, block, etc.

Filters at stock height much less susceptible (you'd have to drive through water as deep as hood).

 

I have the K&N intake and the OEM Intake with K&N Filter and the Air Resonator blocked off. I'm going back to OEM with the K&N filter.
Supposedly K&N has better mid-range and loses some peak power in the top end. For the K&N to be efficient, it needs to be effectively blocked off from the engine bay to reduce heat soak. We use things like tape and foam noodles to block it off but honestly, it looks silly. Pick an intake you like the look and sound of.
You'll gain more cost effective power by changing your exhaust headers and high flow cat.