Not sure if this will do it .....Did you try going into Tools - Options and then under the Document Properties tabs click Image Quality. Try changing the resolution on the slider bar all the way to the right to see if this helps with the output. Another thing to try is go to File - Save as and change it to dwg then at the bottom click on options. You can try to check "High Quality dwg Export" and maybe try "Export all splines as splines". If it is what you want you can then save the dwg as a dxf. If none of them work try playing around with the settings to see if you canget something you can live with.
Hope this helps!!
I had a somewhat similar problem, which I talk about here:
What I ended up doing was creating a drawing from the part file and exporting the 2d curve from there. The resolution is excellent, and my machinist is able to project the paths onto the part surface in his software to generate the 3d curves.