You seemed to be asserting that without a major user near the dam, they would need to build more transmission lines or otherwise waste the generating capacity available.

This seemed unlikely to me, as transmission grids are built with significant redundancy, especially for the high-voltage networks. For example, the transmission capacity for the 8 500kV circuits from Bruce Nuclear (ignoring 3 230kV circuits) is 1.5 times the generating capacity. I wasn't sure about this particular station, but with a bit of digging, it seems like the Massena-Adirondack lines alone (there are several others) can carry 900MW, which is more than the capacity of the power station. So no additional lines should be needed.

I can't be that much since we've had long distance high voltage transmission lines for decades, even in relatively poor countries.

Plus, if you really wanted to because there was no other use, you could, you know, shut down the hydro power plant and return the land to nature. Hydro power plants still have an environmental impact, no point in running them for what is practically, speculation.

In the US, the people who pay for those lines are the consumers and it isn't cheap to run. This translates to more expensive power bills.

Shutting down the dam isn't going to happen. It is split by Canada and the US and does more than just power Coinmint.

The lines are cheap enough to run. About 1-2% of the electricity cost in the UK.