The Porsche purist will tell you to never modify your Porsche but there is another group that says you can always tweak it and make it better. My personal opinion is based on the car that I own. If I had a 356 and it was original, then I would do everything I had to keep it that way; however, my first Porcshe (996 C4) was heavily modified (exhaust, cats, headers, tune, cold air intake, interior changed to alcantara, wheels, etc..). I loved working on that car and modifying it. To be honest, it didn't make that big of a difference in the power you felt behind the wheel but it did make some and the noise/sound, was worth it to me. Here are some pics of my old 996.