On my Nikon D7000 RAW files, I use DxO to PP. DxO automatically brings out details in both dark and light areas. As far as I can see, Auto-DR on the X100 does something very similar: it analyses the scene. If it sees high contrast areas, it ups the ISO selectively, that is, it raises the sensitivity on the dark areas of the image to bring out more detail. That's why the ISO on this is 800 (4 times the base), to get more detail in the very dark areas: the door with the 'Restaurant' wording. The rest of the image, the X100 leaves at ISO 200.
Try a few test shots with high contrast scenes: it works very well indeed and saves a lot of work in post.