Between Anger and Survival, Welder is pretty much strictly superior to Trash For Treasure in every way possible. So, since you don't actually need the ability of Trash, you have to compare it to other cards you could run, like disruption.
I won´t argue that Thrash for Treasure is better than Welder but since in a format were almost every Deck has a way to kill Welder Trash for Treasure could be a secondary way to get an artifact after a Thirst of Knowledge.I can imagine that the Control Slaver variants that splash Black could add Entomb in the Maindeck to support Trash for Treasure.The list from Smmenen that I recently saw on SCG used a single copy of Crucible as well as a Strip Mine.So entomb might not be a that odd choice.TfT(heh) would also interact with Intuition.
I am not claiming that it should deserve a MD slot in Control Slaver/Goth Slaver I am sure that it definatly should be tested.
On TnT:Since this Deck can win without Welder Trash for Treasures seems unnecessary to me.Instead of Trash for Treasures it used Survival which is a better choice since it can guarantuee you a long term pressure on your oppenent while the single creature you get with TfT can easiely be Sworded.