I had a chat with a photographer in his gallery recently and he showed me one of his earlier landscapes (before Canon 5DII). I, having been infected by an incurable disease, otherwise known as pixel-peeping (stemming from a prolonged exposure to Internet photo boards), couldn't help noticing "huge" blobs of chroma noise. He then told me that is one of his bestsellers. Customers (non-photographers obviously) were delighted by the painting-like impression the image creates, similar to pointillists technique (think Georges Seurat), when viewed from an appropriate distance.
Moral of the story? Noise or grain does not hurt that much if it fits the subject. In your case, I agree with you that it somehow works with the shot. If you print it on a canvas, it will be even less obvious.
As for the origin of grain in scanned transparencies, it is mostly because of a hard light in most non-drum scanners (similar in effect to condenser vs. diffuser enlargers). Hence, if you want less grain, go drum.