Well let's see, the color variation in the barn looks more like camo than different boards having different amounts of weathering. Do the color variation per board. Also I think if it was weathered the red would be a little paler, not pale, but paler. Also I think you should darken the barn area so there is more contrast with the fireballs and with the light above the doors. About that light, an oil lamp sitting on some crates might be more appropriate. You could also have some hay barrels, broken farm equipment, or something else besides the tires to break up the line where the building meets the grass as the tires are flat, dark, and therefore blend into the background.
The barn door has no visual seperation or any kind of shape to it and the arrangment of the boards to indicate doorness: it looks like an extruded section of wall. Maybe use an X arrangement on it and trim on the edges. The hinges melt into the wall and are hard to see.
The lighting on the right silo has a blue tint to it in the center of the highlight that looks weird. Also it has a secondary tube shape coming down the side that doesn't reach the ground...not sure what that is but maybe have it's mouth angled towards the camera. The lightness of gravel might looks nice on the road.
All in all it's a nice scene but I think the barn is weird looking regardless of the spec map. Maybe post a new screen.
Oh one last thing, the top window of your barn would be more interesting as a door as they are used for loading/unloading hay barrels. They also have a small crane arm with pulley often.
Look at the wood on this barn:
[Blocked Image: http://www.tommckay.net/wp-content/uploads/2009/05/old_barn.jpg]