Wow I totally thought you were actually representing the Factor value of the node with how much "filled" it was. Maybe the opacity of the fill could be the factor. So current design would be when Factor 0, fully opaque when Factor 1.0 or when a node is connected to the Factor input.
@venomgfx that's sounds very interesting, as it allows the curves to be much more readable and provide an extra information that is intuitively visible.
But if the factor is very low, would it still be visible that the node is active ? (Will there be enough contrast ?)
Some opensource Photo RAW editor uses a soft light gray line in the outline of the curve, it draws Grid in dark gray. As here in Blender the grid is light gray, maybe a curve outline in some dark color helps better visualization?