I'd say go for it. You never know when it might be useful. I'm a voice/data network engineer and I never bothered learning it. Right now, I need to learn it. It would do wonders for my job and career
Absolutely, apart from automating it is a really powerfull scripting language for Windows Admin. If you know some other scripting language it won't take long.
I come from a Linux background being "forced" to work on Windows now so I always loved the command prompt, powershell made Windows just so much better.
I use PS a LOT. I spend a lot of time with Microsoft System Center products, and I use this more than the GUI most of the time. If you are in a Microsoft environment, or tasked to manage one, I reckon this in an invaluable skill to have.