The FCEUX Nametable Viewer is a great way to capture those slightly off-screen map portions. Also, you know how in some games, there's a large portion of the map that's moving while usually the ground stays stationary, like with some Mega Man bosses? Usually, the seem between moving and non-moving portions is a bit off and you can lose a scanline or two of graphics but with the Nametable Viewer, you get both portions without any distortion.
And as for your revised map, it's vastly superior to the original. And personally, even if the darkened palette is intentional and used to set up the mood of the game, I think the map works better with bright colours.
