I'm looking at a getting an 2003 6 speed coupe. It nice and in the price range I'm looking for, but it doesnt have an "aero" package. I'm wondering how big of a difference that has on performance, what it is besides a spoiler, etc.

 

this is merely cosmetic. no performance difference.

 

Don't let the lack of aero pkg hold you back. It's a trunk spoiler and two small underbody aero pieces. I think these things improve the drag coefficient by 0.01.

Just get an OEM spoiler and install it yourself. Very few cars come from the factory with the aero pkg because it's so easy for the dealership or owner to install later since not everyone likes the spoiler.