I love the Core Worlds, the worlds colonized before Contact.  People who lived without gravtech built them, and many are still alive today thanks to the Peloran Treatments.  That gives many of them an amazing sense of community, but they are very much colonies of Old Earth.  They are Earth In Space if you will, having far more in common with Earth than the Outer Colonies that came after them.  They’re old.  They’re comfortable.  They’re powerful.  And they’re stagnant.