Tech mining is incredibly capricious when it comes to output.
The size of the ruins improves the chances of getting something 'big', but doesn't guarantee it at all.
It's usually worth mining any size ruin.
And it's always worth running the mines until they say there's nothing there - I've seen tech mines pull colony items out of ruins that were almost entirely dead.
It's basically Starsector: Gacha.
The haphazard nature is exactly why I wouldn't want Ruins become an important factor in colony selection, since you can easily get disappointed with the rate or the nature of the finds you get from it. Though I've got an idea how to make Tech-Mining stay random while not feeling bad as an Industry.
Imagine an Industry that has different output based on market conditions, while chiefly being focused on the effects of the Ruins condition. The industry would have an output comparable to the current Tech-Mining if it was build on a market with the Ruins condition, perhaps Ruins would also have a negative hazard rating if untapped that decreases as the Ruins are progressively being explored. However, the Industry would also have accompanying effects, such as increasing population growth on a colony with Decivilized Subpopulation and eventually removing its hazard modifier once growth is no longer possible. Possibly also preventing the Pollution condition from appearing on habitable worlds with a nanoforge installed. It could be named something along the lines of "Infrastructure Melioration" and justified as a resource-hungry method of removing and preventing man-made planetary damage. Maybe it could also reduce the demand for drugs on worlds with mining to better justify its usage outside habitable worlds.
What do you think?