Always a pleasure to watch something be built by wood. The Yak is coming along nicely guys. Nick on the lead in video of you in the bay/ocean which spray jacket are you wearing/
The best trick I know for spoke shaves is to set one side deeper than the other such that you can vary your cut as needed simply by shifting the tool laterally. But I've never used them on fiberglass or epoxy.
Another type of sanding block we use in stock making is a pink eraser with the sand paper wrapped around it. Its is stiff and flexable at the same time and you can ususally get it pin pointed to the location in need.