I have over 600 strange coins, and over 50 three of coins on each character... So no, they aren't useful to me... Not to mention that all that Three of Coins seems to produce is duplicate items of what's already in your inventory... Rare items have no purpose being included in the drop table for activities that are allegedly in the same level of difficulty as the raid... It's a waste of time... I'd have had 10 times the chance at something useful if I had taken the time to run Court of Oryx instead.