settings for automatic weight painting

I have a troublesome model, and hand-painting weights is tiresome and error prone. I would like to have the option of adjusting the settings for automatic weight painting to be more or less precise. An example would be to set a lower setting, allowing me to then expand any selected vertex map to expand the influence. Also, if I "Lock" any given set of vertex maps, I would like to then run "Automatic Weight Painting" to only affect unlocked Vertex Maps. This way I could increase, or decrease the influence of newly selected Vertex Maps, without losing the settings of already correct Maps. Smoothing of weight groups to ease transitions would be helpful for Unlocked Maps, while protecting already established Maps.