I would pass on the extended warranty. According to Consumer Reports, plasma TVs have proven to be very reliable. Any problems will more than likely occur within the basic warranty period. For calibration, you can start here for the basics. You can spring for a calibration DVD if you want to take it to the next level.
I started out with nothing & I've still got most of it left M60 VP160 QS8 EP350 M22 VP100 Algonquins