I agree with rodslinger, it's unlikely that my car will need $1300 worth of work that isn't already covered under the GM 100k mile powertrain warranty that comes with the Sonic.
That being said, I can't predict the future, and have no guarantee that my financial situation will be as stable for the next 5 years as it is today. Even if the cost of a covered repair is small, the cost of a rental car can quickly exceed the cost of the repair itself. I don't have an extra car just sitting around, so this warranty gives me peace of mind knowing that not only will my car be repaired, but I don't have to worry about being without a car while it's in the shop.
I justify it to myself by looking at what I spend in a year on full coverage for my car. It's around $1300. For the cost of 1 year's car insurance, I have 5 years of repair and rental car coverage (loopholes excluded), which is cheap peace of mind in my opinion.
If you have a cushion in the bank and substitute transportation readily available, you likely are wasting your money on an extended warranty. If you're like me an budget yourself to within an inch of your life, it's worth having that peace of mind.