Currently, there's no specific reason to go to Gondor Ruins, Rohan Barrows, and Harad Pyramids (the only exception are the Old-Haradric Sacrifical Daggers in Harad Pyramids but they're just slightly better daggers). Yes, there's good loot, but no rewards for going to these places specifically. Black Numenorean armor can be found in other places in the desert, Rohan armor and weaponry are found all over Rohan, and same with Gondor. And plus, you can get an achievement for killing a random Gondorian citizen but not one for killing the risen corpse of a long-dead Gondorian king? There should be an actual specific reason to go to these ruins besides the good loot, and I think achievements for killing the wraiths that protect said good loot would be nice.
"Kings of Old" - Slay a Gondor Ruins Wraith
"" - Slay a Rohan Barrow Wraith
"" - Slay a Harad Pyramid Wraith
"Ancient Sacrifice" - Slay a Taurethrim Pyramid Wraith
Name suggestions are welcome, as I can't currently think of one for the Harad and Rohan Wraiths.