What do you mean by 'upgrades'??
Aesthetic? Functional?
The Boxster
spoiler is the product of wind tunnel testing and functions quite well.
Many of the aesthetic 'upgrades' while subjectively 'looking better', may not actually function as well... at least I've never seen any data supporting this.
Realize that the spoiler doesn't come into play until you're staring at a speedo pointing to 10 o'clock or better.
If you just want it to 'look' cooler, there are several choices. But if you actually want it to
work better, your choices are much more limited.