Do electric wall sockets dry out?

Yes, the plastic in a wall outlet can over time get brittle. I recommend you replace any outlets and switches that are over 20 years old. I recommend you replace them and wire them by wrapping the wires around the screws and not by inserting the wires in the spring tension holes on the back of the outlets. An outlet that is subject to repeated plug ins and unplugging of a device should be replaced every 10 years.