If you're level 69, don't even bother with the dark iron plate for fire resist. Find a smith with Aldor faction and get some Flamebane armor made.
I can make all of it except the helm (and that soon) on Echo Isles, if you happen to be playing there.
To answer the original poster, I think that dark iron lost 99% of its desirability when TBC came out. The quest to learn to smelt/forge it is pricey in terms of mats, and to make anything of significance takes a lot of dark iron ore, and will be quite difficult to sell, as the green stuff dropping in Outlands is so superior to all blues and most epics old world.