I chose to pay up front for service, extended, and ranger purely for peace of mind, especially since a) live a ferry ride away from the service centre, and b) we'll be taking looooong trips and will therefore be covered should anything amiss occur. I get to just put it out of my mind.
However, as the thousands of Model S's get cranked out and we are hearing quality control continues to improve, the value of prepaying does seem to reduce over time. So Tesla seems to have thought through an ultimate mind game for customers: a) do I pay more (usually more than double more) for this car than I have ever paid for a car in the past? And then once you have completed the a) quest, you get hit with b) do I prepay for service for a car that could very well be serviceless?
[At least the product is so damned good it completely heals the brain from its trials. Or maybe it's not healing, it's just the direct electric current to the pleasure centre overrides everything else.]
So back your question, is it worth it... well, I really like the peace of mind. I'm actually hoping that's all I'll get out of it. So far so good.