I wouldn't really call it security by obscurity, you can probably find most of this information already. When I was in high school I had a map of the natural gas pipelines and power transmission lines in my state (public records). Since the forest is cleared for both, they are great places to go skiing in the winter on the hilly parts or ride around on ATVs or horseback in the summer.
The leak to worry about is the priority. What is the difference between a super critical oil refininery and the average refinery? I bet the average terrorist niether knows or has the means to find this out, but now there is a hit list in their hand given to them by the leakers. Going back to my example, we knew we were under powerlines, but is this just some random line to a town or is it THE line to New York City. I didn't know and I didn't care, but this might help answer questions like that for people we don't need or want to be telling.
If that doesn't damage our national security, I really don't know what does.
A power line gets destroyed by terrorists, cutting power to NYC for 3 days as crews work to restore service.
Some member of the public or some journalist might ask "gee, why didn't they have someone guarding that power line if it was alone responsible for carrying power to a major city?"
The answer from officials would of course be: "Whoever did this attack was a fearsome mastermind and analyzed our grid to figure out which lines would do the most damage. Of course now we have the line guarded 24/7."
But the attack still happened. It was in all of the officials' best interest not to do anything prophylactic because they get more mileage out of making a show of dealing with things people are already scared of.
So I'd argue that thanks to the leak, we are all safer from the sort of misbehavior caused by the perverse incentives officials have toward these sorts of things.
How difficult would it be to plan an attack that would have significant consequences for a major city's infrastructure? The New Yorker ran a piece a few years ago on New York's water supply and how it's extremely vulnerable. Surely anyone who spent a few weeks studying the infrastructure of any city would be able to assess the vulnerabilities well enough to determine whether or not an attack made sense.
So given that there are already thousands of things which could reasonably have been determined to be good attack targets, the addition of a list of a few thousand more does not make terrorism any more likely, since there was nothing stopping anyone before.
What the leak does give us, however, is the ability to look at these pieces of infrastructure and evaluate whether anything has been done to secure them. If it hasn't then there is only one direction blame should flow.
The leak to worry about is the priority. What is the difference between a super critical oil refininery and the average refinery? I bet the average terrorist niether knows or has the means to find this out, but now there is a hit list in their hand given to them by the leakers. Going back to my example, we knew we were under powerlines, but is this just some random line to a town or is it THE line to New York City. I didn't know and I didn't care, but this might help answer questions like that for people we don't need or want to be telling.
If that doesn't damage our national security, I really don't know what does.