In the original release of D2:ED there was a random piece of legendary equipment in the chest Lovis will open if you give him the soul stone. In DKS that was changed, but it is still better than the non-reward you would get from the ghosts (though IMO it is worth trying the quest that way just for the dialog options when you talk to Lovis again).
I DKS I talked to Lovis on level 10, but 4 reloads only gave gold and potions from that chest. Returning at level 13 it gave a little better loot; I got offered a warrior head (creature parts showing up fairly consistently IIRC), but after a few reloads figured I wasn't going to get a ranger or mage head. At level 16 it took 3 reloads to get a (level 6) mage head.
There are no consequences for what you do with the soul stone outside of the those two conflicting quests.