Karl one thing I noticed after years using both is that if you really stay focused with the power plan it is more precise when taking off a lot of material...in that if the knives are sharp you can take off even amounts with every pass. Can you do it with a block plane? yes...will it take longer...also yes...

While it is not wood...a good surfboard shaper can take a very rough blank and give you a precision surboard with near perfect symmetry in 20 minutes. A shape that is larger and much more complex in form than a Rudder or Daggerboard. They take full advantage of the ability to remove equal amounts with each pass....every pass they make on one side it duplicated on the other. If you ever get the opportunity to go to the Surf Expo Trade show they usually have a few well known shapers shape boards in a glass fronted shaping booth...they are amazing to watch.

Pete, Thats why I said in the hands of a "skilled craftsman"
LOL. The right person could shape them with a 8" sander/polisher with a "Diskit" and 40 grit/80grit/120 grit paper. In the wrong hands the sander would trash the project in about 3 seconds.