I'm curious as to why it always comes down to 'warp drive' or 'robotic' visitors -
It seems limiting
Without warp drive or some kind of FTL, it would take thousands of years just to reach the nearest star. So you send out robots in a thankless gesture to alien posterity, or you build huge "generation ships" with large populations aboard whose descendants will one day reach the nearest star.
One of the many troubles with such generation ships is that by the time your people get anywhere, they won't be your people anymore. Their culture would be entirely different after millenia in space.