With my Cayman R, it provided a noticeable increase in performance. I have no dyno numbers, but the car did feel more alive.
With any N/A engine, there are minimal gains to be had. Intake plenum, throttle body, headers, etc. each will add a bit. But Porsche does a pretty good job of extracting the most performance they can. Except perhaps with their headers - those are the most convoluted, restrictive things I have seen!