Re: Humans are "Special"
I would say our adaptability and our ability to work together as a group.
In an episode of Babylon 5 that G'Kar talks about what makes humans unique. He siad that if any other race had built a station like Babyon 5, it would have only be open to that race. But the humans, when they built such a station, opened it to everyone. The sense of community allowed them to use the best of these other species to help themselves and others.
Humans are incredibly adaptable to their environment. Most other species in sci-fi settings come from mono-climate plantes, so they are specially adapted to one type of environment. Humans are able to live anywhere. That's why we can grab the bad planets, and use those to support bases on the good planets where people want to live.
Plus, we breed like rabbits compared to several other sci-fi races, and there are always humans around willing to take up available space.
We are a curious little race, with some people always wanting to see what's over the next hill. They seek out the new places, then move on. These explorers are followed by the settlers, those trying to find someplace new, where they can be "free."
Plus, unlike many other sci-fi races, we can find ways to make a buck off of anything.