Brought home a cheap belt sander from Bunnings Aerospace. A test run on previous off cuts shows it is marvellously effective, and doesn't gouge the foam anywhere near as much as the random orbit sander, or even a sanding board. Does the job pretty quickly too.
Start at the PORT tip and sand off the layup! Started with 40 grit, finished with 80. Cleaned up with sanding boards and did more damage than the belt sander did! Removed all the upper skin, other than the PORT tip joggle, and the LE overlap, which I have not figured out how to do yet.
Along the way trim the TE straight and trim the tips.