Concerning the dremel project: Shouldn't it be important that the scratches are unidirectional? A dremel would be circular, or? Possibly some setup with a Fein Multimaster could help.

This reminded me of the British pianist Clifford Curzon, who apparently hated plastic piano keys and, if possible, would rub them over with sandpaper to get a better grip.

Whatever it takes! Playability is the most important thing. But as a bonus these plastic keys also look a lot better with the "brushed" finish.

If I find a way to make a Dremel attachment to speed up the process and avoid disassembly, I'll do my Numa Nero as well. Although the weight of the Fatar piano keys makes the gloss finish less of an issue there.

I dissassembled the KB and removed the keys and gave them the de-gloss treatment demonstrated in this video:
https://youtu.be/31hhHEDIlj8

It involves dragging a scourer back and forth (in this case along the length of the keys) until desired finish is reached. Unlike what's shown in the video, I found I needed to do this in two stages: using heavy duty scourer first, followed by "non-scratch" scourer after wiping the dust off from first stage with a damp sponge. To finish off I cleaned the remaining fine dust off with a damp cloth (forget using glass cleaner shown in the video). The white keys are very easy to do, the black keys take some time as you have to do top, sides and front. But it's worth doing. (But note that you definitely cannot do this properly without dissassembling the keybed.)

The result is remarkable. Feel and playability of the keys has improved 200%. It's still basically a synth/organ keyboard (the action is what it is) but the keys feel very nice to the touch, much easier to play fast, and glissandos are no problem.

Incidentally, if you're on the east coast of Australia, after a cheap ultra-portable synth-action keyboard, these Nektar SE49's are on sale at DJ City stores for $AU79 (in-store price only, $149 otherwise). I'm in no way affiliated.