I mentioned this elsewhere, but I’ll repeat it here. A trick to detect duplicate lines in Inkscape: set all your strokes to something highly saturated, like full red, with a low opacity. Any duplicate lines should show up as a darker shade.
Also in that thread is a link to an Inkscape extension that will remove redundant path segments. The original works for exactly duplicated segments; my modification consolidates points that are up to 0.1 px apart.