Well, I just installed some washers between the cones and the bottom of my SL1210 M5G. I used what are called "fender washers," which have a big flat area and a relatively small hole. Using an M6 bolt as a guide, I selected fender washers with 1/4" dia. hole (just comfortably big enough to slip over the m6 thread) and 1-1/2" diameter, which is just a little bigger than the top of the Dayton cones.
It did stabilize the table a little more. The feet are less wobbly. But the diameter of these is small enough to fit inside the round edges, and makes contact with the bottom of the SL12x0.
Now, I didn't do exact A-B tests, and for me, putting these washers on and off would be a bit of a struggle, but I put on an LP full of songs I've been familiar with for over 30 years--James Taylor's Greatest Hits on Warner Brothers (Fire & Rain, You've Got a Friend, Sweet Baby James, Mexico, How Sweet It Is...). And I got a sense of going up another notch in clarity, of more space around the notes, of musicians and singers placed in space.
My wife noticed it too when I asked her.
For example, I'd never much noticed the cello accompaniment throughout "Fire and Rain" until I started listening to it on LP again in the past year. But when I listened today, I didn't just hear the cello, I heard more of its characteristics, such as the scraping of the bow across the strings (but still in the context of an overall integrated sound). Before, I'd hear the cello; this time I felt its presence.
You may call me crazy, and it could be my imagination, but at least it only costs $1.15 to find out for yourself.