To image something like the roadster on a Planet orbiting Vega (~26 LY away, furthest star anyone on Earth could visit and then return from in a lifetime) you're looking at lenses greater than the orbit of Pluto, ish.
Optics/Physics is a bitch here. To really see/prove there are aliens running about, they have to screaming at the top of their lungs for a very very long time, hoping against hope that anyone will hear. It's just really really hard to build equipment that can passively listen for accidental broadcasts and spy on alien cars. At least under our current understanding of physics.
[0] http://hosting.astro.cornell.edu/academics/courses/astro201/...
It is not necessarily true that more time is spent aboard a ship than light would spend taking the same path, as measured by an external observer.
If you had a ship capable of accelerating at 1g indefinitely, then as measured by the crew, they could cross the galaxy in only 24 years.
https://en.wikipedia.org/wiki/Space_travel_using_constant_ac...
To an observer who is self-propelled (and has enough energy), the speed of light (as seen by others) is no limit. It's not like you can fire your thrusters and NOT gain momentum and speed; or that, as you accelerate, the stars start passing by at the speed of light, and suddenly your ship jerks, ceasing to accelerate, because you hit an invisible velocity brick wall.
https://en.wikipedia.org/wiki/Deimos_(moon)
https://en.wikipedia.org/wiki/Apparent_magnitude
Edit: corrected
“A telescope about 51,075 ft (15,568 m) in diameter would be required to resolve the Upper stage from Earth. A smaller one could see him as an unresolved dot, about 98.2 ft (29.9 m) in diameter, in ideal conditions”
So I recon that reinforces the hypothesis.