I thought I would add, that most of the tuning of my 2.7L 2000 Boxster is based on TTP parts
Link to TTP. My intake and headers are TTP and the Autothority chip I am using is based on the TTP ECU parameters. I find it interesting that TTP says that adding their chip, headers, intake and high flow muffler gives a 2.7L 2000 Boxster about 25hp, which is almost exactly what I see on the dyno. Like others have said, getting much of a HP increase out of our cars with bolt-on's and such is difficult and expensive.