Thorns damage in general is underpowered in the game and we're looking to correct that n the future. While we're discussing a number of ways to do this, the favored idea internally is to allow Thorns to benefit from your primary stat (Strength, Dexterity, or Intelligence). So if you have, say, 2000 Intelligence as a Wizard or Witch Doctor, then your Thorns items will do +2000% damage, much like your weapon damage. This is, of course, a huge buff to the Thorns property and there is no specific timeline on when we're going to make such a change.
though we also suspect that simply making all Thorns mechanics deal 2500% more damage than they currently do may be a bit too extreme.
After reading this portion of Wyatt's answer I thought huge buff is correct. A 2500 thorns Topaz will do 2000% meaning 20 times the damage so 50k! Why not have thorns benefit from Vit instead? Those stacking thorns will be stacking Vit anyway, so it's a nice synergy. And Vit is usually less than the main stat. I have 2800 Int but only 800 Vit. With 2500 thorns I will do 70k damage but only 20k when it is based off my Vit.
I mean the main stat boosts regular DPS but thorns stackers don't care about regular dps. They want more Vit and defense.
So 1. Should thorns benefit from Vitality instead?
I also wanted to ask:
2. Should thorns do damage to ranged attackers too?