We purchased our RV in 2007 without an extended warranty and have not had any big need for one. The engine AC compressor and transmission both died, but were covered completely by the Ford warranty. I guess the only other repair that MIGHT have been covered is when some mice ate some engine wires...but that was only about $200.
I guess like any type of "insurance" it is like gambling...sometimes it works out, sometimes it doesn't.
BTW - I tend to fall into the group of folks who do not buy extended warranties and have not had too many times when I have regretted my decision. Although I will look into it when we buy our next unit.