Re: Cowboy Bebop/ Firefly inspired game
One note about the Bebopverse is that almost all of the action took place on planets in the solar system other than Earth, as well as moons of Jupiter, Saturn and Neptune, that had been terraformed to varying degrees. That implies that at least someone has access to very, very high technology. (There are many anime series in which terraforming has taken place where it seems the technology or time wouldn't be sufficient for it logically -- see Armitage III for an example).
Still, it wasn't the setting that made Cowboy Bebop cool, but the characters and the way they interacted. Spike and Faye had a very interesting dynamic, Ed was -- well, Ed, and Vicious was one of the classic villains in all anime. When designing your campaign, the main thing is to give your playerrs interesting things to do and hooks into the setting; just as it always is in campaign design. The most intricate world design is of little gaming use if you can't use it to tell great stories and give your players great things to do.