A Velocity stack with an intake in a high-pressure and cool air location is the only real improvement for an intake.
Having a semi-smooth tract works as well...not totally smooth, as you want some air tumble.
A finish like this works best, did this on my Audi and it works great:
http://forums.audiworld.com/picture.php?albumid=87884&pictureid=101311
before (on left) & after (on right):
after with velocity stack:
Look at what they use in F1 racing...they user every trick that works.
PS: if you look at how much material those spiral/tornado things take up, you can see how much flow is actually being restricted.