Air-raids and city structures.

[Ahriman]

At the same time, just damaging current production as Ahriman suggested doesn't provide any type of long term type of damage to infrastructure

And why should it? Allied bombing of Germany didn't stop its military production from rising steadily.

You can easily abstract the cost of repairing infrastructure into the foregone hammers.

I think reducing production outright is much more effective than just damaging a specific building, which also starts getting messy in terms of UI.