If you want an extended warranty from Dell, or from any other supplier, you may get a more reliable answer by asking them rather than us. Whether the cost is justified or not is a personal decision that only you can make.
I always work on the principle that someone has to make money out of these warranties so the mathematical expectation is that it will cost you more than it saves you. I never take out any sort of extended warranty as I take the gamble that my equipment won't fail and can afford to repair it if it does. Whether this is a wise stance for you is not something that anyone else can answer.