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But, you have to add time for the civilization to go from cavemen to that level of technology, which from what we're seeing is pretty long. And you have to assume they develop alone, uncontested (all spread times increase dramatically, possibly to the infinite when contested). And you have to assume they even want to colonize continuously until conquering the entire galaxy. Then finally you have to assume that either we have the technology to detect them, or they decided to communicate with us on our level of tech.

There are actually more assumptions in the "alone in the galaxy" arguement than in the "there's somebody else out there" position.

But, you have to add time for the civilization to go from cavemen to that level of technology, which from what we're seeing is pretty long.

It didn't take us long. About 8000 years from the end of the last ice age to the present -- more than half of which is recorded in written history.

An a species only has to do this once. The colonists will have their past to build on.

If we assume that colonization proceeds at small fraction of the speed of light, the technological advances made by the home planet will always be available through ordinary radio transmission.

So even if the colonists hibernate during travel, they will wake up to knowledge that advanced while they were asleep.