If you want to deploy a real time app or a socket or tcp server, or even a high load API, you can give Node.js a shot. Node.js can do normal web stuff too, but I don't know any good reason why you would want to learn and use it when you are already proficient with PHP.
For the sake of simply learning it, just go ahead and learn it.
As far as jobs go, outside of Silicon Valley it seems that there is still a huge market for PHP programmers, and those Drupal/Joomla/Magento/WordPress sites aren't going away any time soon.
I'd also recommend Python, which many PHP programmers instantly like. Getting started with Flask (http://flask.pocoo.org/) should be fairly easy. Several big sites like Instagram and Pinterest are powered by Python.
Also it is always great to try new paradigms as they open minds more. So double yes for that reason I guess.
There is a lot of PHP resources on the web; so I don't have you have to give it up.