build into the device a means for consulting the original blueprints
I don't think I understand. For a very small investment, a hypothetical civilization could launch, say, 100 Von Neumann robots (jumbo sized). Upon reaching their target star, the instructions are: gather all available data and then build a copy (scion) of yourself; dump your memory into it and then BOTH head at random to another pair of stars.
The payoff comes when one--inevitably--wanders home, bearing the complete data collected by all of its ancestors. Remember, we are positing very-long-life civilizations, with long-term views. This is a tautology; if it has taken you 100,000 years to reach the level of sophistication needed for this plan, you do not expect to wink out in 100 years and your civilization can afford to wait a few thousand years for a probe or two to come home.
In principle, only one probe might be needed--but occasionally probes will be destroyed, find no raw materials, etc. So you should start with several.
For an ultra-advanced civilization, this should be easy as 'pi'.
Even at 0.05"c", there has been ample time for every star in the galaxy to be visited. If there are multiple advanced civilizations, there should be a traffic jam. In particular, at Sol. And if they are using nano probes, it should be even more certain that aliens will land on the White House lawn. So where are they?
My answer: they are not anywhere. Else we would see them.
--Boris
Possibly because intelligent probes would have their own reasons.