Increasing tone arm effective mass?

The purpose of the penny was to increase tracking force, not effective mass, so this analogy is a red herring at best. There is nothing wrong with trying to increase effective mass at the headshell. The issue becomes the rigidity and the resonant characteristics of the tonearm/cartridge system. Unfortunately, the former does not change and the latter undoubtedly will. The only way to see if you like the result it to try.

Thanks so far. I should have stated that I knew the penny trick increased VTF.

I did it by using one supplied CW instead of two. This puts the weight far fro mthe pivot point with the same VTF. It produced more defined and impactful bass. It does not work on some carts. Different effect on different carts.

Mass added at the headshell will add directly to the effective mass of the arm. Mass added further down the arm tube will have less effect on the arm mass, just like an anti-skate weight. Arm wraps do more for damping then increasing mass, unless it's heavy near the headshell.

The effect on the pivots should be taken into consideration. Some arms can't really support too much increase in mass. Same goes for rigidity and resonance. Hard to make generalizations - arms are very different.