Starships are big
Tom Brosz said:
"I expect that unless we are talking about a crashed Star Destroyer, any alien hardware--if it exists--is not going to be easy to find."
Starships have to be big. A starship must get to at least 1% speed-of-light in order for transit times to be practical. A nuclear fusion powered starship would be almost all deuterium in order to get to 1% speed-of-light. A nuclear fusion reactor would be fairly massive. A simple fuel/structure mass fraction calculation shows that a starship needs to be really big. This line of logic leads to the conclusion that there are metallic objects out there the size of small asteroids that are NOT asteroids.
Gary