It didn't get far ranging into the speculative possibilities -- one panelist urged as a real limit that the four week journey to Alpha Centurai that appears to be the limit of what NASA is working on now. And one said he thought it would last about a generation. But had a lot of fun with the limits and structures of empires. If the transport is the fastest mode of communication, you end up with a central government but strong governors on the colonies.
And if it takes twenty years to go out and come back, how can you maintain control?
Especially if you need people who want to go out
There's also the possibility of a hegemony, possibly dominated by the strongest race.
So why would they hook up? Self-defense if there are aliens out there, perhaps. (If we realize there are aliens out there, expect us to pour tons of money into getting out there so as not to be in a position of weakness.) Disease? There might be no danger, unlike the Americas, because we might not be close enough. But if we are, expect danger.
There's no exports except ideas. You can probably get gold locally more cheaply. Or potassium. Local lack of elements might be the real big problem. If we can't terraform, things get interesting even with colonies. After all, the Americas were settled by people who had free air along the way and when they arrived, and you could survive falling off the ship for a time.
One audience member thought any interstellar civilization would have to be post scarcity, but panelists argue that it all depended on when technologies were invented.
I brought up life extension. A twenty year trip back to bring back a punitive mission in forty years is more of a danger if you have two or three millennia to look forward. Also, it gives a motive to leave: avoiding overpopulation. on the other hand, it gives a motive to stay: you're risking many more years of your life.