Modding the box is a cheap way of increasing airflow(or more accurately unrestricting the induction path). My opinion is that a CAI + shield + pods aren't worth the hassle unless you are producing a race car(drag or circuit) because you shouldn't notice a intake restriction unless you go above a certain power output (250rkw...correct me if I'm wrong ok guys!).
A street car or daily driver would be pretty quick at 250rkw...then just look at improving response instead of power. It's been mentioned elsewhere but I think it was in this order: lightest wheels, lightened flywheel, not too heavy clutch, CF propshaft(a bit overkill but would be noticable).
Also...I'm not a real techie and everything above is my OPINION (I'm just looking at doing something similar to you too!)