If you don't like to work on your sled, don't mind taking it to the dealer to have them work on it, which includes the downtime. You should absolutly get it. It will likely pay for itself once the sled get a few thousand miles, i.e. exhaust, seats tearing, suspension arms cracking, etc. The parts themselves are expensive and the labor to work on it only adds to the cost. Now if you preffer to work on your sleds yourself, are mechanically inclinded and own the basic and special tools to do so, you may want to just save the money and put it towards the potential failed parts. The motor is really the only thing that can't be repaired cheap swiftly. Suspension parts that crack can be welded and even reinforced. Rails are also on a can't repair list but I think it's rare for Y.E.S. to cover them anyway. Clutches are possible but if you clean and change the buttons you really shouldn't have any issues anyway.
I got the Y.E.S. when I purchased my sled, it was part of the preorder deal, if I had to pay for it I probably wouldn't. I only trust my dealer to work on it and they are about 2 hours away. I've brought it to them at the end of each season, to do the repairs. Durring the season when I can't afford to wait, I do the work myself and pay for the parts myself. If your a high mileage rider and have a back-up sled it may work out to get the Y.E.S. if not, it's a trade off.