A free-flowing intake can only help the airflow it it is the biggest restriction in the system. Unless you drive all the time at full throttle and redline rpm, that's not the case. The throttle is the main restriction in the system. The stock intake may be a little restrictive for the high-throttle-high-rpm condition, but if you're there, fuel economy is not a priority, is it?
A short intake is going to shift the intake resonance higher, so it'll help more at high rpm than low. Again, how much of your time is spent at high rpm? not much.
Keep it stock.
For comparison, mine is stock. I think my mileage is ok.
