I really like Active D-Lighting and read an excellent article on it a while back (I'm sorry I don't remember where I read it). It does make some changes to both the exposure and then the in-camera processing.
What sold me on the feature is that I went to a museum when I first got my camera, put it on a tripod and tried all kinds of settings. I kept a notebook with me and recorded all of the settings changes.
I took pictures of an area which was normally lit, but which had a section that was in the shadows. I took the same picture at the same settings with the only variable is I changed the Active D-Lighting setting (started with off, then tried each of the other settings). When off, the shadow area was totally dark. When Active D-Lighting was set to normal, the shadow area was lightened up just right, as if it were shot at a different exposure than the rest of the picture. I really thought it was terrific to have the camera do this as opposed to having to do it in post.
Since then, I have always had Active D-Lighting set. I suggest you run your own tests to see the results.