I'm not sure about making curves renderable. I haven't done this. Maybe email the user in that post. But you can extrude a nurbs circle along a curve that will sure show up in a render. But if I remember right you were looking to keep the geo amount low, so let me know if this is something you would be interested in.
The renderable curves in 3dsmax come from just drawing the curve then checking a "Renderable" box and you can set the radius and steps (detail). The idea being that you can quickly draw high-res wires/pipes.
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