Often, while modeling, I would like more control over graduated transformation of vertices than Proportional Editing makes available. (In particular, it would be nice to be able to have an influence gradient centered on the transformation pivot, changing with distance from it, but affecting only selected vertices.) Some other applications, in effect, make vertex weights available to the edit system, allowing you to transform vertices proportionately to their weight while editing.
Am I missing something obvious? Is there a route to this in Blender?
One solution to the specific problem I mentioned above is to hide all vertices you don't want to change while using Proportional Edit. This has the obvious disadvantage that you can't see what you're doing - even if you make an instance of the object, with no parts hidden, you only get to see your changes when kicking back into Object Mode (when a bmesh is written back to a mesh??)
To me, it seems odd that the selection of influenced vertices is made by visibility, not by weight.