It would be convenient if you could set a hotkey to scale the value of the active vertices within the active vertex group. It would multiply the value of the vertices based on mouse movement or an entered number, similar to the regular Scale transform.
The purpose of this is to increase work speed when modeling with a modifier stack. Lots of modifiers take a vertex group input that you may want to quickly adjust the value on a per-piece basis. The best example of this is solidify. If you could quickly change the value of verts in it's vertex group, you could quickly adjust the size of the solidify effect, similar to Shrink/Fatten. Currently to do this you need to go into Weight Paint mode and paint a new weight.
The Levels tool is available in edit mode and comes close, but requires you to make several clicks to enter a new weight. So essentially I'm asking for the Levels tool, but with Gain based on mouse movement or an entered value, and behavior more like the transform tools.