Yeah, it is mass but as I said above, work out the moment of the force over the two fulcrum points (saddle and nut) on the "clockwise moments = anti-clockwise moments and my (average) difference of 0.003% plastic to brass applies.

The lack of give in brass as opposed to plastic is just transferred to squashing the bridge wood that bit more. Damping is damping is damping. The exceedingly short length to saddle leads you to one conclusion; you can make far more difference at the headstock end if looking to changes in tone is your aim. Far more to go at, especially lateral movement through the length of the nut.

Brass pins can look good, especially with bronzed strings.

Whatever floats your boat. Changing from one to another includes altering more than just the density of the pin to make those differences. I am no expert on guitars per se, but on things I do know, mainly vibration and propagation of waves, I remain fascinated by the pseudo science in guitar magazines, forums etc.