Are body modifications like flared rocker panels and ground-effects
spoilers just for looks, or do they have benefits like increased
traction and/or reduced drag?  

I'm thinking they just change the looks.

I've been comparing the Boxster S to the Boxster S Anniversary Edition
and notice that the anniversary edition has all the options that
increase performance, like stiffened suspension, shorter gearshift
throw and larger wheels.

But no aero kit.  And I postulate that if it helped performance, they
would have included it.

However, the anniversary edition also includes the PSM (Porsche
Stability Management) which probably *reduces* performance in some
situations (in the nicest possible way, of course), so my posit could
be wrong.

Sorry to bring up nitty-gritties.  I am in a phase of life known as
Boxster Waiter and have 3 more weeks to kill before taking delivery of
a Boxster S Anniversary Edition (silver exterior, black top, dark-grey
interior, Bose, CD changer, cruise, and seat backs painted silver).

BFMartin