Just one other thought to throw in. If you have a given range of elevator travel with respect to the tailplane, an increase in longitudinal dihedral by increasing the leading edge down incidence on the tailplane will allow a further forward c.g. limit (as the tailplane will generate a larger down force for a given AoA) whilst maintaining essentially the same degree of control. Therefore, the aircraft may be flown with a greater static margin or a greater degree of longitudinal static stability if longitudinal dihedral is increased. So, to go back to Dick's original question, an increase in longitudinal dihedral allows an aircraft to be flown with a further forward c.g position thus resulting in an increase in static stability.
Perhaps we are into the semantics of the English language?