Processing single channels

I don't think that will help much, AFAIK the general component output format is RGBA, even for Extract RGB (it will simply be distributed as e.g. r,r,r,1 for red). I think you will just be adding unnecessary processing.

There might be something to gain by combining different grayscale sources via Assemble RGB (and perhaps Set Alpha) if the sources need the same processing, but it is highly dependant on the actual construction (you might end up making it slower) and rendering size (generally the larger the rendering the better this trick work if bitmap based components are used in the intermediate combined processing)