I think I see what your getting at, I thought you meant polygonal surfaces, not polylines. I haven't tried it but it might be a good idea. I have done plenty of sweeps in ACAD (ask Tim about my flexible tubing
). I have also used thick colored splines in 2D drawings to show wire routing in very complex control panel wiring diagrams. But I don't think I ever used polylines or splines in a render.
Why don't you try it. Save a file with plines, then render it. Then "Save as" a copy and extrude a circular profile along the pline. Save it and render. Post the results and let the crowd see how it turns out because I am intrigued now. Tim will tell you I really like finding shortcuts like this, even if I don't use ACAD much anymore.
Also, this is the only ACAD tip I remember. If you have items that are not selectable, hidden, or just plain not there but they are keeping you from purging a layer, then use qselect to select everything on the layer. You can the delete it while it is selected. Tim and I had some files that had this problem. We would try to purge layers but for some reason they wouldn't purge. Then I learned about qselect and it took care of the problem. That is the only tip I remember about purging.