Mathematically speaking the noise in an image actually contributes to a reduction of resolition of an image. You can't make out individual specs of sand on a picture of a beach when there are grains of noise for example.
An important notion, of fundamental importance in the telecommunications world (as revealed in the work of Shannon and Hartley, for example).
But in the digital camera case we must note that the signal to noise ratio varies with the luminance of the specific pixel (duh!) .
Thus, except in the "shadow" areas of the scene, a decrease in noise will not lead to a "measurable" improvement in resolution.
So the point you make is important with regard to "resolution in the shadow areas", but not much elsewhere.