
Good news about this in Cartographica 1.4:
For those who need to trace, the new snapping function provides a simple mechanism to make sure that your new features line up with edges or vertices of existing layers, or with a specified grid.
As for the lack of visibility, If you haven't already done so, go to the Cartographica > Preferences and change the Edit Backdrop Color to be less opaque (reduce the Opacity slider) or change it to entirely transparent if you don't like the isolation effect from the backdrop.