If you have the ability to travel between stars, it doesn't seem like there's still need to conquer a planet for resources - except for resources that aren't natural.
For example, you can easily just get water from comets/asteroids, mineral resources from uninhabited planets (easier than to fight the inhabitants), and gas/fuel from the gas giants.
However, one resource you cannot get is slaves. Therefore, i predict that any advanced civilization that can travel between stars would actually invade to capture the life forms as slaves, rather than to extract resources.
I think if you have the ability the travel between stars you probably also have machines to do work way more effectively than using human slaves.
Maybe they could use humans for a zoo or something.
Well as two armed slaves, we'd be useless at handling their devices that require all 8 tentacles... We might not even be useful as snacks, having picked the wrong handed proteins. They might annihilate us out of frustration and build a hyperspace bypass instead.
For example, you can easily just get water from comets/asteroids, mineral resources from uninhabited planets (easier than to fight the inhabitants), and gas/fuel from the gas giants.
However, one resource you cannot get is slaves. Therefore, i predict that any advanced civilization that can travel between stars would actually invade to capture the life forms as slaves, rather than to extract resources.