I'm surprised at the remark on microballoons and silica ... And, I think you meant microspheres. The white fairing mix is glass microspheres and the purple is phenolic microballoons... confusing terms. In any case, I find the opposite to be true. Microspheres (white, glass) needs less silica to make it non-sagging (thixotropic) and feathers out more nicely ...when goopy or when cured and sanded. I prefer it. Microballoons (purple, phenolic), doesn't seem to want to become non-sagging without adding more silica than I prefer, which makes it harder to sand. It doesn't appear to produce as smooth a finish or as fine an edge as the glass microspheres. That's my impression anyway, and admittedly, it's a subjective kind of thing and someone else may believe the opposite to be true.
In general, I will do my earliest fairing with microballoons, or anything that will be glassed over with additional glass is faired with microballoons. Once the boat is sheathed and faired once with microballoon, then I will fair with the white glass microspheres ... intending it to be a final fairing. If I've "got religion" on the finish, I have used the WEST System plastic mini-fibers for fairing in pin-sized scratches prior to primer and paint. I think System III sells plastic minifibers now too.... but since they can shrink in heating/cooling cycles and can 'print' underlying layers, it's best to use it for just the finest scratches ... and it feathers out beautifully.
Your close-up fiberglass pic is perfect for showing the pattern of bumps that results on glass right after it's first cure. You should take another pic of the glass after a light sanding with 100-grit to show how it just takes the tops off (without getting into the glass) and produces a surface that is much easier to fill with a fill-coat of epoxy.
How'd the shrimping go?
bd