I find lots of good questions in this discussion thread.
The first question of whether or not to use the AR foam spring damping needs to be answered in the context of the spring used.
Second, I am intrigued by rwij's inquiry regarding the isolation of spring grommets.
Just as we ponder tonearm resonance with a cartridge's compliance (spring) one has to consider the same attention be paid to a sprung turntable's suspension. They are the same.
Less mass requires less spring. Also, the more compliant or softer the spring, the lower the resonance frequency.
bauzace50 mentioned the AR may have a suspension frequency of 2 hertz. Nice. This is really good thing for steering clear of any tonearm resonances just a few cycles up the scale. There is also probably some other benefit with regards to Bass performance although I'm not qualified to say.
The AR is definitely a low mass affair as compared with other suspended designs. As such, it would make sense that their springs are softer. It is for this reason, along with the fact their reciprocating parts aren't of the same precision as Linn, that I feel it is important to use proper damping of the preferred OEM AR suspension springs when using an original AR.
Grommets lead to yet more thoughts.
Following what AR did by trying to decouple their springs from the spring stud/hanger is typically what is seen from all manufacturers of these sort of turntables. SME uses lossy O-rings, Oracle uses sorbothane etc.
The lower spring mounts that I've seen from AR are works of art IMO. Semi-lossy material with a carefully aligned shield for insulating the sponge spring damper from the spring stud. Upper grommets were not used because I believe AR glued their springs into place on the T-Bar for perfect alignment by positioning the spring's ends so they pointed at the center of gravity of the T-Bar. (A nice trick for setting up an AR is to sharpie pen a line along this part of the spring in order to better point them towards the CG as well as eliminate any obvious torsion for pistonic movement) All of the spring isolation was done solely by the semi-lossy adjustable lower grommet.
This area of grommets may be worth exploring in terms better spring isolation.
Isn't this fun?