Light colors certainly open a room up and make it feel bigger. To achieve the height effect you want, you want the lighter color on top. Going darker on top will appear to shorten the room. Also, note what furniture you have in that area. Big, dark furniture will tend to weigh the room down. If this is the case, consider using lighter furniture in that area, or, minimalizing the furniture along that wall all together. As far as the molding you would like to install, using the same color in a higher sheen will add a nice, subtle architectural detail.
Hope that helps,