To be honest, I still want some in-game mineral generation, for moderate amounts.
This is more for roleplay purposes rather than as a meaningful substitution to expanding ever outward.
Iirc TN minerals are supposed to somehow "condense" over long periods of time, and mostly in large planets.
You could have some very large planets (or who knows, black holes? and gas giants) have a small production of TN minerals every year to simulate that.
Once again, I'd like this as a flavor, roleplay thing. I'm not suggesting such a high generation of minerals that would reduce the need of expanding.
And it would create a few interesting situations, like:
This system is full of dirtballs. But a couple of them actually make some minerals every year, and they're close to the home system, so they're actually worth at least considering taking.