Only in bitcoin land would a 30% yield be considered low.
At a flat 30% yield, not compounded, it will take 172 weeks to break even.
How confident are you that they will be around in 3+ years? How confident are you that they can maintain that yield?
That's a good question.
I think their next gen chips will give us the answer we're looking for. If they're able to keep up with what's coming online (BFL, Avalon and those that are deploying based on their chips) as well as the dark horses in the running (KNCMiner), so then they'll remain a going concern. If they can't, either their chips aren't efficient enough or the others just dump so much power on the network that they can't regain their position, then obviously, that's a problem. Which makes the current price level seem accurate. They can't be priced as if they're out of the running because they're not. And they can't be priced as if they've pinned down their future, because they haven't.