I have an SL1210 M5G, and pretty much every tweak I've made improves inner clarity, dynamics, and lowers noise floor. These have included the fluid damper, a sorbothane (not sorbogel) mat, Sumiko or LPGear ZuPreme headshell, brass footers, thick plank platform, and shock abosorbing footers under the plank. I recently swapped out the Vibrapods under the plank for a pair of plank-wide thick gel pads. They're actually gel wrist rests for computer keyboard that I got from Office Max. I estimate they further isolated the turntable from room noise by about 1.5 dB *over * the Vibrapods.
You will also lower the internal noise of the SL12x0 series if you get some factory bearing oil (I got a tube from KAB) and lube up the spindle bearing. Easily the best $4.95 you can spend to improve the performance of this TT.
By the time I did all those things, the cumulative effect on the SL1210 was transforming. The combination of quart-controlled direct drive and these vibration control and isolation upgrades has made for a dynamic and rhythmically compelling presentation.