This commercial that UPS ran back in the day claimed that they washed their planes because it reduced drag.
That should make their planes fly faster for the same throttle setting.
Seems like the same would hold true for washing our Boxsters.
"A clean Boxster is a faster Boxster."
Plus, it's more fuel efficient.
https://www.youtube.com/watch?v=Mk8BhQEuzyI