I fyou'll be depending on Atkins as your only 3B, be careful. Atkins numbers have been consistently dropping in the past few years. Not weeks, not months, but years. There's very little confidence in him right now in both baseball and in fantasy. Yea, he could rebound, he's not old. But he could also continue to decline. There's also a fear that if he doesn't improve, they could get rid of him, thus taking away one of his bonus features (playing in Colorado). If you'll have other options, and Atkins is just a possible positive in the trade, but a guy you can bench for now, then it's a pretty good trade.
Torre loves Ethier, but with Manny on the shelf, I get a little concerned about his production - you'll have to take the risk on that one.
I would pull the trigger if you can balance out your team for benefit.