Do you have a 2 or 3? With a 2, unless things have changed, you have up to a year to buy the apple care. But with a 3 you have 30 days for the apple care plus.
One advantage of the plus, it has 2 instances of accidental damage repair for a $49 fee. Which, if your child drops it accidentally, can save you hundreds.
If you have a 2 and regular apple care, you can take your time and decide.
I bought it after I had one instance of a bad 30 pin port on mine. Fortunately it was within a month, but I figured the extra $100 was worth having coverage incase my replacement suffered from the same thing.