I’d vote to skip rather than overdoing it. But, if your pipeline is near-lossless you might be able to render it all twice - once for everything BUT overlay, then a separate project to add film grain?
I wish I could say that this’ll work, but alas, I already tried something like this with my Last Jedi fanedit. The quality deterioration was visible, and I never took the second project any further than reviewing it myself. It’s a nice idea on paper, but I don’t think my work is near-lossless enough.