Trace-over works for me. Plot-ready raster to vector conversion remains a
dream. As G-Rock has taught me, get your raster file aligned and make sure
your horizontal and vertical lines are truly horizontal and vertical. Use your o-snaps.
Create layers and use them. Draw with combinations of the simplest elements you
can get away with. Do it in 3-D if you are clever enough for that (I am not...Gene Rock is!)
The more "unusual" stuff you use (double lines, poly lines with "width", splines, etc) the less
"transportable" it will be in .dxf format to other CAD programs.
Dave