>>At reativistic speeds, time dilation makes it reasonable for ( One-way) trips of only a few decades. Given a longer lifespan, this would NOT rule out any visitors (just bring along the family, or fellow colonists).<<

Lets assume that you are right. I don't think it at all likely that the nearest star system is inhabited with sentient life with technology that superior to us. So lets be very generous and say that they are coming 100 light years instead of four and the trip takes 200 years real time and say 30 years subjective (dilated) time for the crew. For a round trip it would take 400 years. Everyone they know at home would be 400 years older, when they got back. the crew themselves would be 60 years older.

Given that level of sacrifice does anyone else think it unlikely that they would come all the way here to buzz airports and stick probes up hillbillies' butts?