If they aren't authorized, that would likely mean their service isn't either, so technically speaking, I can't see how their warranty would benefit you?? That is the pesimissic view of it anyway. If it gives you a little piece of mind, then it would be worth it, but I'd probably be on the same side of your thinking and go without it. OR, shop around authorized dealers and see what kind of pricing you can get...
Thankfully, I haven't had to use it on my receivers, but I have had to use it on my integrated amps.