Check this
http://986forum.com/forums/showthread.php?t=23706
Specifically the posts by Cartel. He has done this to a 3.2 and is very happy with the mod.
Or this.....
http://www.planet-9.com/cayman-boxster-modifications/49945-installed-ipd-intake-plenum-986-boxster-pics-review.html
This one was on a 2.7, but would still be relevant since you are wondering about the effectiveness on smaller capacity engines (ie sub 3.4).