I love export option! In fact i even did this render of city i exported, althought i have found some small issues model.
1) City wall exits have faces that are clip through each other
2) Walls also can be cliped inside themselves sometimes, it is pretty annoying
3) There are long random triangles where the roads shoud be, but it is very rare, i had this glitch only once
Anyway, here is my render of cardboard city generated with your wonderful tool
First of all, this render of yours is VERY cool! Can I share it on my Twitter (with credits of course)?
About those issues - that's how the viewer works. I don't have many tools for procedural mesh generation (in Away3D), so, for example, a gatehouse is just three boxes combined without trying to clip anything. I probably can (and should) fixes gatehouses, but walls are harder. If you take a look at exported mansions you'll know it can be much worse :)
Everybody likes it: https://twitter.com/watawatabou/status/1390042322855989251 :)
On my next iteration I'll remake gatehouses properly. This 3-boxes thing is copied from Toy Town. It was more or less my first 3D app ever, I can do a bit better now.