I spent some time this week working on the spalted top. I figured that if I couldn't sand it smooth because of the thinness of the veneer, then it was worth trying to fill the holes instead. For this I made up a maple saw-dust and oil mixture.
It might be hard to see in the pics, but here's some before shots of some of the worst crevices
And here's an after shot - the holes have been filled, allowed to thoroughly dry, lightly sanded flush, and then the whole surface has had a couple of light goes with truoil and 400grit sandpaper
Sorry the lighting is so different in the 'after' shot, but hopefully you can see how well it worked