The TOS Movie collection is definitely a mixed bag. Only 1-3 are watchable, and while 2 has a nice grain structure, it's blue-shifted. A good comparison between the "before" and "after" would be to compare Spock's funeral in 2 and 3, specifically Kirk's close-up, as well as the TMP stock footage in 2.
It seems like the DNR in 3-6 gets progressively worse. 3 is satisfactory. 4 is borderline. 5 is pretty bad. 6 is miserable.
I notice in Star Trek V, the contrast has been boosted to the point where "God" is totally invisible in the pillar of light in some of the shots.
For Star Trek III, there's only one time in the movie where you can see film grain, and that's on Genesis when it's snowing. I guess they had to dial it back, otherwise the DNR would wipe out or blur out some of the snow.