It's worth it if you use the warranty. A little while before it's up (about 6 months or so) make a claim that the picture quality has greatly decreased since you bought the TV... because in most cases, it does, so it's not just fraud.
To be honest, it's a bit under-handed, but they will probably replace your TV because a decline in picture quality can't necessarily be fixed, unless it's like a projector where you can replace the colored bulbs.
Point is, most people get these warranties and forget about them because they don't think that even the slightest thing wrong with it is worth the effort of getting it fixed. If you get the warranty, make sure you put it to use.