I'll feel i got my money's worth if the panel lasts at least a decade
Chances are the tv will be shuffled from one room to another a number of times during that period. One tv gets tossed, another in the household takes its place, so on and so forth. Still have a fully functional 27" panasonic crt, going on 15 years now. Folks don't care/don't want to invest $$$ into a larger hdtv.
My current computer monitor is a dell 30", circa early 2007. Still works well. Also have a sony 19" lcd from 2000 or 2001. Has some issues detecting inputs and returning from standby, but no picture issues.
If you can get a good deal on an extended warranty of 3-4 years, sure, why not. Otherwise, cost of warranty will be similar to that of a single repair visit, give or take.