Well, it turned out that using 3x3 pieces threw a bit of a wrench into things -- I hadn't dealt with that before.
But I've made some progress. Here's my first track layout:
http://dungeonprint.com/images/oval-track.jpg
More later...
(FWIW I use Blender nearly exclusively, so I'm sorry to say, I don't have any insight into OpenSCAD problems. However, I've found prints of 4x4 and larger are way more subject to edge-lifting issues [not to mention bed size limits on cheaper printers], so it doesn't bother me personally to use smaller tiles and clip them together.)