I just discovered the free open source program called "MeshLab", which can be used to visually inspect 3D models on modern computers.
http://meshlab.sourceforge.net/
If someone else hasn't already done it, I may take a crack at trying to output "stl" files from Maxima.
"stl" files are extremely simple": ordered triples of ordered triples describing oriented triangles in 3D.
There are lots of stl files available on the web to use to test this program; most of these files are used for 'printing' 3D objects.
I'm kind of surprised that gnuplot doesn't already hack stl files.