[Fletcher]

There is alot of conflicting information on this topic. I have been doing research on this for months. I do not claim to know it all but I have owned several p-cars and have modified several (excluding 911's, I do like them though). ECU mods are highly subjective, on any Boxster extracting more than 6-8 h.p. is highly unlikely. I have spoken to a couple of tuners who will add there tuning into the mix probably this year. Headers, intakes, cats, all could be viable options when tuned correctly. Here is my take one by one:
1. Headers. I have read many positive things about this mod. By no coincidence Porsche has added very header like manifolds to the new Boxster to aid in power increse. Used in conjunction with ecu and cats this may be one of the best mods you can buy $1300-$2200. headers vary quite a bit in price and looks. Some offer almost no merge collector while others are longer. Scargo and speed art's headers are very short while dansk are longer.
2. Intake. Well you could fit a BMC filter, or a complete cold air intake (the evo seems the most popular). You probably will only gain a couple on top with the BMC. The cold air intakes need to work with ecu to get any real h.p. though. Although I have no personal experience with them I like the scargo unit the best. It is of course the most expensive option as well but is multi shaped carbon fiber and I hear is not as loud as the evo (fine by me). This mod should be used with ecu flash.
3.Cams. Very little out there on these so far, time will tell. I am not a big fan of cracking the motor open unless it is way out of warranty and going to be raced, or needs serious work. Could be very viable though sacrificing some torque. Dyno's will tell the story on that one. Being in Ca I am always wary of smog regs as well.
4. Cats. A worthwhile mod when used in conjunction with headers, ecu etc. I am leery of 100cell cats though. The 200 cell are a seemingly better option (we want some backpressure right)!. Also California cars would want dual o2 sensor fittings on the cats (supersprint and Roock offer these).
5. ECU. Wow like the headers many choices out there. GIAC and Powerchip are probably the best known. Unichip is a piggy back type that hooks up in line. I am still doing research on this topic. You can make power, it's not going to be huge though. More tuners to come though.
6. Tuning packages vary wildy and many european packages don't use anything wild on the intake side (just a BMC filter) hmmmm, I find that fact very interesting. See Roock, Speed-Art Etc). However most seem to use headers/cats/exhaust in conjunction with a filter and ecu. 20-25 h.p. should be available. Rob at scargo told me he could get me an honest 25h.p. with his headers, cats, intake and ecu. He feels as many do that an exhaust change just isn't worth it for minimal or no gains (many times losses).
Just my two cents. I will probably focus on my supension, interior this year and performance next year. All it takes is time and money.

p.s. One last though about superchargers for the Boxster. Has anyone every been happy with one of these that fit right didn't send cel on a regular basis and not least of which ran right?