My speakers are from 1989, they get Howards wood care on them. They look almost new after all this time. Also use it on most of my vintage MCM furniture.
Spray on a MF towel, wipe speakers, buff off, done. Do it every couple months.
The bigger question is how do you keep a piano black turntable clean? If I look at it, there is a smug mark, even after I clean it, there is dust. Will never get a piano black TT again!