Matt_Stevens said:
I will say it again... Taking a currently released Blu-Ray and adding grain to it is just adding noise.
To state that adding grain is just adding noise may be technically correct but it's a gross over-simplification in terms of how added grain can create the appearance of more or enhanced detail.
A great example is this comparison shot from emanswfan's 70mm Filmized Concept project:
http://screenshotcomparison.com/comparison/39951
To simply dismiss the benefits of this kind of enhancement (carefully applied) is just foolish, particularly when trying to recreate the look of film in a source that has been DNR'd.
And yes, Cameron stated in an interview that all the grain had been completely scrubbed from the new Aliens master, so it's a reasonable assumption that the grain visible in the current BD has been added.