What you describe is just a Pen on a pen tablet.
In my experience, emitting pressure on the same pointing device is - quite exhostive and faulty. Not speaking, that if you handle pointing device to be pressured well without altering pointage, then you can assign 4th value to it (brush depth or brush size?). It is in the end about will to soft calibration, but each artist is compromising between his idea and work exhoust, or its smoothiness and flex.
What you describe is just a Pen on a pen tablet.
In my experience, emitting pressure on the same pointing device is - quite exhostive and faulty. Not speaking, that if you handle pointing device to be pressured well without altering pointage, then you can assign 4th value to it (brush depth or brush size?). It is in the end about will to soft calibration, but each artist is compromising between his idea and work exhoust, or its smoothiness and flex.
Agreed, If you want to use the full pressure range, you will have to press hard for higher values. But most good applications will give you the option to adjust the curve, you can do that in the Wacom System Settings AFAIK, and then you also can just increase the strength of your stroke in your application (which does only take a second in 3D Coat Sculpting for example).
All this can be done, without needing the second hand off more important tasks, like using modifier buttons (alt and ctrl... couldn't live with that in 3D Coat for example), or always being ready on the space navigator to rotate / translate the model in no time while the pen hand does not need to do anything (you can even work in some applications with the Pen while the Space Navigator moves the model under your pen).
This will be highly subjective of course.... but I rather take some additional steps to prevent fatigue than taking my off hand off my space navigator. Now, I still need to find out how to bind ctrl and alt to that damn two buttons on the space navigator that I never could get to work, then I reached my personal 3d modelling heaven 
