I haven't tried long exposures on the new Ektachrome, but I shot a number of night scenes with the old formulation (mainly VS). This was with my OM4T which does OTF exposures up to 4 minutes. The results were always great.
I've always had a philosohpical issue with "reciprocity". For timed, night scenes the whole nature of the light is different. Whether it is a campfire, city lights, or the cold hearted orb that rules the night the rendering of colors is fundamentally different. The notion that the film is failing to render accurately seems very subjective.