Sounds good. You were right as in Crossroads Part II we found not one, not two, but four cylons at important positions on Galactica, although not the ones you guessed.

It would be interesting for them to reach Earth, and find ruins (with Daneel Olivaw on the Moon a la Foundation and Earth), or as they approach Earth, encounter space junk.

An Earth origin would explain the mismatched technologies and the preponderance of 21st century Anglo-American culture in the Galactica universe. That's the only way the most annoying pecularities of the show could be explained. A Von Daniken Chariots of the Gods arrival in Earth's distant past would make no sense at all.