My Spec Boxster is not set at the lowest ride height allowed by the rules. At the lowest height, the shocks will occasionally hit the bump stops and there is a lack of suspension travel which reduced grip. I also run a bit of rake (front slightly lower than rear).
Yes, there is a cost to the higher ride height in terms of increased aero and weight transfer but these costs are less than the benefit from greater suspension grip.
For others who might read this, remember that Spec Boxster's have PSS9 coil-over shocks so the ride height is fully adjustable (which is not true of the stock suspension).
Here is the Spec Boxster rule on ride height:
Section 4.H
Ride height minimum 90 mm front and rear as measured at front cross of aluminum cross member and front-to-rear braces near rear sway bar.
Here is what my car looks like from the side (low but not slammed):
