Dodge Nitro

I wouldnt take any of todays spark plugs past 30K miles in any car. You are only hurting your vehicles performance. They may look ok... but they are not.
We have seen some plugs come out of newer vehicles with only 20K miles and they were shot. There are a lot of factors involved. Its better to replace and be safe. (thats only 9 years working with the "newer" cars talking so maybe I am full of it too ;) )

-RPM