It really depends what you want. It is difficult to get a much better setup from coilover kits because Porsche is well known of designing and testing their suspensions very very well. A coilover kit has the advantage of adjustments to certain tracks, a huge advantage if you're racing your car. PASM or not PASM? Difficult to say. I would probably choose it, especially on the Boxster. The only disadvantage of PASM: you can't install a coilover kit if you want to.

And if you're more into looks (much lower ride height)than into performance, PASM is the wrong choice. On the other hand, the Boxster isn't actually made for racing and going for coilover kits which lower the car too much could have a serious impact on chassis rigidity, roof mechanism and noises.
From my past experience, I would stay with Porsche suspension setups. When I installed the H&R coilover kit on my 996 Turbo, I loved the setup. But afterwards I drove the Porsche sport suspension kit for the 996 Turbo and I've been shocked by the PERFECT setup compared to the H&R coilover kit. If I wouldn't have sold my 996 Turbo, I would have removed the H&R coilover kit and gone for the Porsche sport kit.

I know that many people believe that installing a coilover kit will enhance performance but they couldn't be more wrong on a Porsche. Stiff and low ride height doesn't mean that a car handles better on the track, something especially amateur race drivers still have to learn.