Pros and Cons of Platter Mass

@lewm , you need to add motor torque to that list.

I think as everything in life there has  be a balance and it depends on what type of drive is being used along with it's performance. The best direct drive motors do not require as much mass as the best belt drives.
Mass does not protect you from rumble. It might lower the frequency a little but you are also adding more thrust to the bearing, increasing noise and wear. 

How much mass is required? Whatever it takes to get the best performance and no more.

It is becoming more common for manufacturers to use a magnetic thrust mechanism. No ball and no thrust pad. Spindle wear is much less of a problem because of the greater surface area involved. Here, lubrication is quite effective if the bearing is designed properly. My subwoofers tell me there is most definitely less rumble with magnetic thrust bearings, at least the one I am using. 

Magnetic thrust bearings also allow more platter mass without increased wear. The same is true of real air bearing turntables. Frank Kuzma redesigned his big table with an air bearing and increased the mass of an already huge platter by about 1/3rd. I wonder if all that air rushing around increases noise. What if it blows on the tonearm?