It's shit now and t won't get buffed.
Players posted new suggestions in Diablo 3 community: improve damage of Thorns. Early in the Beta, we’ve seen the power of Thorns. And there were even videos of players killing Skeleton King through damage return of Thorns. However, after the Beta, most players don’t think it’s useful, especially in Inferno. Besides, for ranged classes who have to avoid damage like Demon Hunter and Wizard, the stat is much less useful.
It's shit now and t won't get buffed.