Here's my opinion:
The extra warranty is worth it for the situation when you might pick-up an object or nail in the sidewall which cannot be repaired and the extended warranty will replace the tire for no charge. However, I think the extended warranties are time limited at 2 or 3 years (look at the fine print in the warranty).
In my case, on my other car (1997 Lincoln Mark VIII) which only gets driven about 4000 miles per year I ran out of extended tire warranty long before the tires need replacement.
I am currently getting ready to replace the 25,000 mileage original tires (Continental self sealers) on my 2006 Magnum R/T and have decided to go with the Michelin Primacy MXV4 tires (approximately $160 per tire plus tax etc.).
From the experience with the MXV4 Michelins on my Lincoln...smooth quiet ride and a low rolling resistance I am going to go with the Michelins on my Magnum. It may be just me, but the low rolling resistance thing seems to me that the car coasts better and longer than the original tires...hope this makes some kind of sense to you.
Let us know what you decide on and how they ride and handle.