Thanks, all, for the 3 tips above. mkriggen, I'll probably end up with a new selection and follow the grits upwards like you do, although I also don't mind if my knives look a bit banged around too so I don't need the polish perfect. Hadn't thought of the fritz idea either, a product I haven't tried.
Just as a side note: I burned on 2 handles this evening and included some beeswax in the handle hole (to strengthen the handle and protect against rust - see youtube) and of course there was the usual amount of hot molten wax flowing out making a mess, and I got to thinking about handle sanding and buffalo horn and wood sanding again.
I couldn't find a picture to link to, but perhaps others have seen images of decade or 2-decadge old, heavily used yanagiba, with worn down repeatedly sanded handles - so worn that they end up with this hourglass shape where it's hard to imagine how wood still survives around the tang, while of course the shinogi looks destined to rendezvous with the spine within the week.
Anyway, my theory is that pro yanagi users in Japan sand their handles a) for 'hygene' and 2) with the wood fresh, to maintain more friction in the grip. Would be interesting if anyone else had some knowledge or impressions about this. Those worn handles do look odd.