I understand where you are coming from with this. I also have a 2001 Boxster base and never even tried an S. Why? I felt that the base had sufficient power for me and lower fuel consumption. The question for me is that I don't have the opportunity to use all the power of an S. I don't track mine, don't do autocross.
To take this principle to the extreme if you get a Miata and drive it to 60 mph it is actually a lot of fun . Try that in a Boxster S and you will be jamming on the brakes to hold it back(I would imagine anyway) and you will be constantly exceeding the speed limits.
However the S may have better brakes, clutch and handling etc but I never explore the limits of a base so why would I want an S? My next car might be a 2009 base - the one without an IMS. In the meantime I am happy with my 2001 base.....
