i think  a node that would be very practical is a node only about shadows.
for example the diffuse node and specular node have all shadows inside. but they  are connected to the lights intensity.
a node only for shadows would be ideal for some ''effects'' inside shaders.

another node that would be practical is a node that is like the specular node. but again not connected to the intensity.
 for exampele bagginsbill a lot of times is using effects with those nodes. but because they are connected to lights they have to be tweaked.

plus in the last days i have been using a lot of times lights with only shadows. but since poser doesnt support this function i have to use 2 lights. it would be very nice if we would have an option to only cast shadows from lights.