Sorry to bump the thread, but I was able to install blender2crystal without going to the Web site, by digging through this Ubuntu repository for it:http://externos.grupoikusnet.com/deb/crystalspace/
I realize that normally, it's a big no-no to use Ubuntu repository content within Debian. But I figured that in this case, since most of the code is in Python, it should not do any harm. And I followed the instructions, for how to install it to Blender, which means that it should really only affect Blender. Even so, there was/is some risk, since the instructions tell us to do a 'make install' no matter what, which could screw up my Python setup.
In any case, blender2crystal works for me now, as this screenshot shows:
I'll see later, whether the rest of Python still works for me!