Getting smooth curves:
Since Pantograph is working from a faceted model, you’ll never get true smooth splines (believe me, I’ve been trying to figure out how to do that!). With some quick work in Inkscape, you can vastly improve things.
After ungrouping the drawing (Shift-Ctrl-G), you will be able to select individual polylines
Hit Ctrl-L (“Simplify Path”) until you are satisfied with the smoothness of the curve. If there are multiple overlapping linesyou may need to smooth both.