[Perfectlap]

your case aside, consider coil overs if you are tinkering with the suspesnsion.
That way you can adjust the ride height in addition to rebound.

Otherwise its a potentialy expensive crap shoot:
Stick in new coils (springs), pay allot of money to the mechanic dude, realign the car, pay allot of money some more for an overpriced Porsche dealership alignment and say a little prayer and hope your are happy with the ride quality and feel in urban driving. Because where you drop it, is where it stays. Or you can pay some more money for un-installing and realigning=waste of money.

with the coilovers you can even make the ride quality softer than stock, make a few adjustments and in height and carve up the DE with the PCA.
Personally, I think the factory got my BoxsterS PERFECT right out of the box. Although sometimes I wish I could raise it from the cockpit. 18" wheels are 18" wheels.