Dave,
Sorry I didnt chime in on this sooner, I didnt notice the thread.

The top of the HT rudders where the wear is in your pictures is pretty solid. There's some foam up in the head of the blade around the edges. So you can grind away that spot with the gel coat crack and still have material to work with when you repair it.

Next time you need to fix them try white Marinetex. Its basically thickened epoxy colored white, and it matches the white gelcoat color that Bimare uses pretty well.

I've filled the holes on my hollow Bimare blades and they dont seem to mind it, I dont believe you ever have enough pressure change to hurt them unless you are trailering your boat over the Rocky Mountains or flying them around in your airplane.

The castings are soft aluminum and they are probably wearing out too, it might be time to make a mold for new carbon ones.