I didn't read the Django or BTTF2 parts because I haven't seen those movies, but I mostly liked the other stuff. However, in regard to your Star Trek point, don't you think they'd want to do everything they could to avoid waking up Khan's crew and getting blood from them after all of the trouble they had with Khan himself? They had Khan readily available, so it makes more sense to use his blood than the others.
Also, wasn't the whole point of Khan's character that he was the leader of the others because he was superior to all of them in terms of his genetic engineering? It's hard to say whether or not the blood of the other crew members would have even had the same effect.
I realize that it's kind of a silly scenario regardless of how you twist it, but come on, it's Star Trek, there's always an element of silliness