i have a 2002 wrx that is all stock. no upgrades....do i need a aftermarket intake or will a stock air box do just fine?

Everything needs aftermarket anything

 

But seriously you might notice a slight improvement in hp, gas mileage, etc. Where you will notice it is if you plan to take it a step farther with exhaust, injectors, and so on. So it really depends on what you plan to do with the car.

The stock intake box is not that bad. Mine makes over 300 hp with it. If you do go with an aftermarket air intake it won't do much. If you get one be sure it is one with the same diameter inside as stock or it will thow off the maf scaling and it will run lean without tuning.