I supposed that the extended warranty is from Harvey Norman or Best Denki kind of shops. Well, it's good to have. At least some years down the road if the cam is no longer working properly and the spare parts cannot be found, you can chose another cam and given the vast improvement in technology, I would think that it'll be worth it.
To the contrary, I don't think it is worth it. Look at the prices for used cameras today and you will realize how much they have dropped and even if you were to sell your camera in a good condition, it is not going to fetch you anything near to what you paid for it.
I have a little more faith in things I buy and despite the usual one year's warranty, I usually use them way beyond this period and for most of the time, they really give me trouble free operation for many good years. Ask yourself how often is it that things that you had bought broke down within one year or for that matter three years after the date of purchase. I am an optimist.
When my camera breaks down, I won't bother to repair it as I will take this opportunity to buy a new one as I am likely to get a new one anyway even if the camera were still working.
After 1 year, sell your camera while it still has some value, then get a new one.
Unlike film cameras that you can use for 10-15 years and beyond, digicams get obsolete very quickly. The depreciation rate is so steep that at the end of the 3rd year, it becomes so low in value that it's not worth the amount that you paid for the extended warranty.