yeah the yellowing would probably be bad for allowing the bands to be seen through the surface. polycrillic as you said you were using might do better. i guess i havn't made anything that is old enough to see the yellowing effect. with the polycrillic did you try sanding it then applying a fresh coat? not sure if it would fog from the paper, but i think there is a fine enough grit to accomplish that, or even could you wet sand it like you would a car's paint?