Very Thin Lines
In order to make very thin lines using 3D Stroke, some tweaking may be required to make them look really good. Naturally, the Thickness control should be set to a low value, like 0.5. The strokes may appear aliased (jagged) when doing this, so here are a few tricks.
First, set Feather to 100. Then increase Adjust Step under Advanced. Finally, Internal Opacity can be lowered.
This should produce very nice thin lines. The apparent downside is that if the camera moves in close to the lines, they may not look as good. The examples below show the difference (magnified by 200%) of the default .5-pixel lines and adjusted settings that yield nicer-looking output.
Standard Thin Lines (Thickness = .5, Feather = 0, Adjust Step = 100, Internal Opacity =100)
Adjusted Thin Lines (Thickness = .5, Feather = 100, Adjust Step = 175, Internal Opacity =92)