For the sake of preserving an authentic 'feel', the grain level should perceptibly increase on opticals. It would actually seem false to me if it didn't, knowing what I know of the processes through which the film was made.

Looking at the recent -1 release, it's obvious that the increase in grain during opticals on a projection print was quite huge. For a source with much less generation loss like Legacy, it will be significantly lower. But after having filtered it out via difference signal, if you put back in the grain that all your prints have in common (ie, what is on the negative itself), we'll be able to see this type of increase, and it will feel authentic while still looking much better than any version ever shown in theatres.

I absolutely hear what you're saying about doing a film-out, though. Doing this could unify the entire movie visually and 'glue' it together as one organic, real final product—similar to how some people who mix music 'in the box' like to break out their digital multitracks into the analog world and let them be summed together and mixed down as real electricity, rather than remaining as 1's and 0's the whole time. If it was me, I would keep the original grain and do a film-out: in this case your digital files are your 'negative', and the print becomes the sort of 'interpositive' which is more final. (Yes, I understand that's not a perfect metaphor, since interpositives are made using different color and contrast processes, but it holds up reasonably well.) This could even be scanned back into the computer to maintain a digital record of what the film medium itself did to the image.

Well, that's what I would do, anyway.