For me this would be a no-brainer: keep the S.
I like my cars as close as possible to stock and in close to perfect shape. Mine is an 01 S as well that came out of the factory with the Aerokit I bodykit and the Sport Classic II wheels. The interior, even though is not full leather, is in MINT condition, so is the body. No dings, nothing. The one thing that was bothering me, the stone chips on the bumper, I took care of two weeks ago by having it completely sanded/repainted. I went the extra mile by repainting the whole hood that only had 2 chips on it.
Yes, I am that anal about the car.
Next time it is in for service I am probably doing the clutch (as I already have all the new parts), RMS and IMS.
The only non-stock parts on this car are the airbox and the CPU that was replaced with a Powerchip (and I think stainless braking lines). According to the tests done by the previous owner, with the cold air intake and powerchip the car has now something in the 285-290hp range. I did not dyno test it myself but apparently the previous owner did.
These are simple things you can do to get more power out of the 3.2 (and the IPD Plenum as mentioned).
I would never trade mine (or yours in such great shape with a full leather interior!) for a car like the one you mentioned.
Sure if my engine dies tomorrow than I would consider a 3.4/3.6 on it but if that never happens, it will have the 3.2 on it for a very long time. Given I have seen many 3.2s out there with 150,000+ miles as mine is only at 40,000 now, it will take me at least 20+ years to reach that.
And in 5 years I am giving the Boxster to my son and as he saw me taking care of my P-Cars over the years I am sure this little guy will stay within the family for several years to come.
Keep yours man. You will regret and possibly cry if you trade it.
CR