Can an old Thorens Table be "Over Dampend" to the point where sound is adversely effected?

Dear Raul,
I was not even thinking about "massive turntable platters" at all.
For what it's worth, I was talking about the overall structure in the most general terms.  Re "lead" (the metal, Pb): I think constrained layer damping works very well based on personal experience.  This would lead (the verb "to lead) one to favor a sandwich of disparate materials that do not differ to much in coefficient of energy transfer among them. Beyond this clarification, I don't want to get too involved in this discussion, much less get into an argument with you which can only lead to the accusation that I love distortion.  I think or thought we both favored unsuspended vs suspended turntables.  Anyway, I do.

This is one of those discussions where only a few of the participants are in learning mode, and the rest of us find an opportunity to trot out our own pet beliefs.  Such is the nature of this hobby, and it's fine.  So, here's my opinion: You can divide turntables into two types, those that were designed to be acoustically inert in the first place and those that were designed to flex in some sort of controlled mode that theoretically would contribute to the "sound" of the whole system, in a positive way (Linn, for example) or would improve isolation from the environment.  The latter group includes all suspended turntables. And all of the latter group would be sensitive to aftermarket modifications of either the suspension or the suspended parts of the table.  Obviously, if you add damping to the sprung chassis, you increase its mass, and this has a secondary effect on the suspension, because it's "seeing" a bigger load.  Conversely, if you impede the action of a spring suspension, that too will have an audible effect.  All of the foregoing can get to be very complex, if one were able to see it as an engineering problem.  This is why I have grown to prefer unsuspended turntables designed from the outset to be acoustically as dead as possible, which usually means high mass.  Like Atma says, this would include the system from tonearm to armboard to plinth.  Halcro did some great things with massive external "pods" for mounting the tonearm, and that seems to work fine, too.  For turntables in this category, we don't need no stinkin' damping, at least no additional damping beyond what is inherent in the structure.