Strictly speaking, we haven’t yet found ruins next to Col 70. We’ve found Braintree sites, but no ruins. There might be ruins that just haven’t been found yet, but it might equally be part of the apparently ruinless synuefe Braintree bubble. The ruinless bubble is interesting in of itself in terms of possible Thargoid/Guardian interactions and might be tied to Melville’s hypothesis of the Guardians having had a forced migration away from an original bubble.
On the second point, as it now looks likely that a route could have been found to the Regor sector using the earliest hyperdrive tech, it’s also worth noting that it’s fairly plausible that Regor would have been a reasonably early target for a scientific exploration mission, being by far the closest and brightest W-R star, and one of the brightest stars visible from Earth. The Regor sector’s also permit locked, which wouldn’t be in place for no reason (it’s a supernova candidate admittedly, but only the 6th closest, so one would presume the other 5 candidates would have permit locked sectors if that was the reason). IMHO, it’s exceedingly likely that this is not the first time humanity had encountered Guardian sites, and that it’s just the first time it’s become public knowledge. The same is implied in Premonition by the Club feeding Canonn with ruin locations to keep them distracted from the Thargoid side of things.
In terms of trying our tech in the Thargoid sites, most things were tried IIRC. No reactions reported on here at least. I don’t know if all the real esoteric items were tried, but Soontil Relics definitely were, with no reaction, implying they were fakes after all. AI Relics and SAP8 Cores were suggested but I don’t know if anyone tested them in the end.
On the weaponising of the Guardian Relics, I’ve always assumed that it was something to do with whatever the relics are made of (or possibly whatever what’s inside the Relics is made of). The store descriptions mention them glowing with some Ethereal energy. I’d originally put it down to them being an extremely potent energy source, and hence drastically increasing the effectiveness of weapons they were mixed into, but that doesn’t really make sense as the effectiveness against human tech isn’t similarly boosted. So, for that reason, I’m going for an extremely potent (but non-reactive) energy source that radiates primarily in frequencies which resonate with Ammonia molecules and hence specifically damage Thargoid organic material.