Pull caps of keys, switches and pots, disassemble, submerge in warm water a while to soften the crud, clean with a soft sponge, wipe dry, place under blower to evaporate the rest of humidity.
No alcohol needed except for particular non-water-soluble dirt.
Clean the board using vacuumer and brush.
Reassemble.
After that it 's like new.

Sweet. You made that sound easy. I’ll report back with photos.

Oops, forgot to mention to use soft detergent, just which you use for dish cleaning.
This will soften and remove fatty cruds (finger dirt, coffee splashes etc).

Usually I only need alcohol for marks from ballpen , rubber "scratching" etc which don't dissolve in water.
And alcohol sometimes dulls plastics irreversibly, which can be annoying.

These are undoubtedly what one should do in cases like these (I’m lazy) but I didn’t get as far as really scrubbing it all down and bathing everything in a bubble bath. Some q-tips, toothpicks, a spudger to remove the caps, isopropyl alcohol, an air blower and a handheld vacuum and lots of kitchen towels and I’m pretty happy with the results. Now I just need to find some retrobrite…