In my experience it has been worth it. After my warranty ran out I needed a new key module, door sill replacement and trunk strut within about 3 months after purchasing it.
Here is information on the service plans from Tesla's web site. http://www.teslamotors.com/service#/service-plans Tesla Service includes •Annual inspection (or every 12,500 miles) •Replacement parts like brake pads and windshield wipers (excluding tires) •24 hour roadside assistance •System monitoring •Remote diagnostics •Hardware upgrades