SLICK is garage kept, I changed the cabin filter at 30K miles and it looked like new. I may change it in a few years when I hit 60K.... I can see if you kept your coupe outside how the filter could fill up with bugs and critters requiring it to be changed frequently.
Gary

 

Never changed mine. If it gets dirty i will clean it and stick it back in.

 

Mine is stuck outside. No issues here. I replaced it 30,000 miles ago when I bought the car. The new filter, after a year and a half, is a little dirty, but nothing terrible.

 

Mine is still original, now at 45K miles on an '04. The air coming in through the vents is still just fine, so I'm not going to change it. On a scale of 1-10, this is a 1 in terms of importance to me unless my car starts to have issues with airflow through the vents as a result of obstructed intake filter or if the air coming in begins to develop a consistent odor.

 

When it smells or when flow is reduced. I'd say every 20-30k. My mom runs the ac all the time and her filter gets smelly every spring.

 

Immediately after my car sat for 12 months outside. It was rather amazing at how much could get into a stationary cars filtration system

 

Changed mine out today. I bought the car in January but had no idea when the last time this filter was changed. He's how mine looked:



Not sure how that nut got in there!
By the way, this job was VERY easy, after watching that DIY video.