Extended warranties: a license to print money IMO, wouldn't touch such with a barge-pole, especially anything to do with Subaru. Anyway, I have a set of Tein Superstreet coilovers two of which need servicing. If you can get them sorted for less than the cost of a new set up, you can have them for nothing. The condition they are in might be better than your shocks anyway. But definitely DO NOT replace them with stock. I can't believe they sell them for £350 each! That's a scandal!