Personally, I would make Tech Mining a structure instead of an industry and let it supply metals, rare metals, and supplies at a low level based on ruin size, not market size. If vast ruins only gives base 4, then Tech Mining as a structure can't supplant the industries, but it is a nice boost early on.
I would tap them regularly early on if this were the case. The pittance of weapons and blueprints at Vast only just barely makes it worth exploiting later on due to cost, when I usually ignore anything smaller altogether.
Like SafariJohn says here, making it an industry improves the chance I'll take advantage of it.
For one, Tech Mining should export a small amount of Supplied/Metals/Heavy Machinery/Ship Hulls. This is due to Tech Mining always creating these commodities without fail every month, as well as the possibility to find derelict ships in ruins.
Also, as ruins are tapped by Tech Mining, they should add growth and income multipliers to colonies depending on the percentage looted and extent of ruins. This could be due to the conversion of ruins into tourist sites(creating income) or using them as bases for new infrastructure(which leads to greater growth).
I don't see why it couldn't do all of these things. We're not talking about supplanting real industry, colony items, or story points after all, but if you were lucky enough to roll Vast Ruins on a half decent planet, not only should you be able to take advantage of the derelict tech laying around, you can bet scavengers would treat it like a space age gold rush.
This is just a "would be nice" kind of thing, but a colony item for resetting the decay for finding useful baubles once it runs out would be an interesting find. A fleet of little search drones or a high tech satellite with advanced ground penetrating sonar or some such thing. Extending the life of it would be a cherry on top.