I just have a CAI for my car, which was labeled as a 2.3; I do know most of the 2.3 mods fit the 2.0, and you're right, the ones that don't just take a little tweaking to fit, but am I wasting my time modding a 2.0? The 2.3 seems way more responsive...
I know, I could just buy a new car, but I've test driven a Scion tC, Celica GT, Eclipse something or other (a fast one), and a Mustang GT; everything besides the Mustang was... strange, in comparison to my focus. I really enjoy driving my car and don't want to get rid of it...