the current situation where even a simple section of wall results in 6 seperate objects in blender.

For real? Which version of SH3D are you using?
I'm using 6.6a and I get no "o" lines in the exported object, so the whole home is seen as a single object when importing into blender. Am I missing something?

In case it wasn't clear I exported an obj file, and manually added the "o" to test the theory, and it works. Theree's an attachment in the linked ticket that has the "with o" test file I've been experimenting with.

If you get a single object, you need to examine the options as I mention in my previous comment. You likely have "Keep Vert Order" selected.