There are many juicy targets like that, whether it's power plants or airports or dams or bridges or whatever. We don't typically worry about hardening them against smart munitions. If you're in a hot war with an adversary like that you're pretty screwed regardless.

There's just no practical way to harden all of it against attack. And a tiny chance of some hypothetical future war isn't a good reason to choose a technology (combusting fossil fuels) that's gonna kill your own citizens every year, guaranteed. Why do your hypothetical future enemy's job for them?

Attacking a nuclear plant on purpose will be seen as similar to attacking with a nuclear bomb in the eyes of the world.

If all you want to do is to knock out the electrical system of a country, you can use an EMP burst bomb over that country, and the grid will be down for months.