I believe I thought I suggested this about 3 years ago.
Why not vary the weight of the brush interactively as you paint?
Like for example;
Left mouse for paint, middle wheel for varying brush weight.
Currently the system means if you want to paint realistically with varying brush weight. to paint a few inches would require going back and forth to the - or + sign to vary the weight. A single brush stroke could take you ten minutes this way? So why not do it interactively some how as you paint?