So many of these can be traced to the Berserkers, who were well on their way to wiping out a whole galaxy. Many think the Planet Killer from Star Trek: TOS was based on them too, and it did eat its share of planets.
Daniel: "Sometimes I forget you're no longer the little girl I used to give piggy-back rides to, Zoe."
Daniel: "I don't care that all your friends have cell phones, you're not getting one."
Daneil: "You be back home by 10:30, young woman or you are _so_ deactivated for a week."
Zoe: "I suppose that pony I wanted is out of the question, now."
Zoe: "I think we should discuss that increase in my allowance one more time."
So why is it so popular in TV SF? Well, first of all, TV SF always has aliens who look like humans, because it's much easier to find actors to play them. And of course they are played by hot, TV-star humans, so the question of sex comes up. But it's the purest fantasy, not really SF.
The one exception in your list is Hera. Her mother's DNA was derived from human DNA some 4,000 years ago in that show, and that makes breeding potentially possible -- there's a recent common ancestor. Hera could never have bred with the natives on our Earth, of course, as Adama himself says. Baltar's explanation of divine intervention is necessary. (One of the sucky parts of that ending. It would have been much better if Baltar had said that God must have taken people from our Earth long ago to start the population on Kobol. That would have made much more sense.)
I wrote an essay on these questions here, because so many people cling to the Battlestar Galactica plot of 1978.
You can find it at: [ideas.4brad.com]
Now, as to the question of Battlestar, it is not at all clear that the new series is a Panspermia story. Moore, the producer was asked this question after season 1, and he said it would not be such a story in his blog, but he was going to try to write a story to merge the ideas of the old show and the scientific non-reality of recent panspermia.
There are two possible options now, since the "Earth" they found is not our Earth (since I am pretty sure our real planet was not named by Cylon colonists.)
1) This "Earth" is given that name, to match the old show's quest, but is not at all our Earth in any meaningful way, not the same culture, no fossils in the ground, etc.
2) There is a real Earth out there, as shown at the end of season 3. One growing opinion is that we'll see it, since the stars in the scene of the Cylon civil war are exactly the Earth stars, and aside from a few related scenes, those stars are not seen anywhere else, including on "Earth" the 13th colony.
But we'll see. In the meantime check out the essay.
It was revealed quite early on in the show (in the Tomb of Athena scene, where they saw that the flags of the colonies were patterns from the Earth Zodiac) that this show is not going to follow the nonsense-plot of our planet being a colony of some other system, with humans evolving off-Earth. That may have been the plot of Galactica 1980 but fortunately Moore has let us know in a variety of ways it's not the plot here.
Mankind originated on Earth (duh) and this is all taking place in the future. Of that you can be sure. The 13th colony is just a legend used to cover up the truth in their mythology. Just what sort of future is something for more speculation.
That leaves only the dead, the virtual and the robotic.
I've thought of a couple (non-popular) choices that could make a great ending.
#1: The Final Cylon is the "Virtual Being." You know, the most popular character on the show for many viewers, usually played by Tricia Helfer, sometimes by James Callis, once by Rennie (Leoben.). The character nobody thinks is the final Cylon because it's hiding in plain sight.
Why does D'Anna not believe this character is in the fleet? Because she saw it as Baltar, her lover. It isn't Baltar, but she thinks it is.
This character is closely tied to the Cylon god. This character is probably the main programmer on Earth who created the original AIs that became the Cylons. Other than as Shelley Godfrey, this character has not yet taken a physical form. I would guess it might take the form of Six as this is the form most viewers know for it.
2: Ellen Tigh. Ellen and Saul have been lovers for over 4,000 years, since they first fell in love, as humans, back on Earth at a Hendrix concert. They and 3 others uploaded their minds into computerized form, and for 4,000 years they have had an on-again, off-again marriage, sometimes ending with Saul killing Ellen, sometimes with Ellen killing Saul, sometimes other ways. Their love story is painted against the history of the artificial human/cylon race, and after many repetitions, this is the final chapter.
Are these stories good enough?
More details on them at my battlestar blog, [ideas.4brad.com]
It is laid out in the credits of the first episodes. They look, act and feel human. Some of them are programmed to think they are human.
Including all the colonials, the people you think are human.
They are all cylons, all artificial, came from Earth long ago. They can't tell the difference because they are programmed not to, and there isn't really one anyway.