I must dispute your fanciful logic chain on this fanciful topic in concluding that the Oort cloud would be the perfect place for clandestine human base. What? As far from Earth as you can get and still claim residence in this star system? When--in my branch of the fancifulizing--you're struggling to even get off the Earth's surface atop a string of exploding nukes?

Granted, if you're fleeing the Earth, like Khan, you'd want to get as far away as possible. But then, like Khan, why stop at the Oort?

No, if your plans including staying in the general neighborhood, I'd say logically you wouldn't get too far from Earth.

And perhaps it isn't the "pure SETI" perspective that makes the asteroid belt archeologically attractive so much as the same perspective as over on my branch: It's a close place to hide (our system's "Badlands") that's not Earth.

I have to admit that in terms of sheer wonder, not to mention avarice at the thought of advanced technology, the alien fanciful hypothesis is definitely the more interesting. You can only take the Iron Sky genre so far before it becomes just late steampunk.

But they did have some neat uniforms.