I think all of these mining stocks are undervalued. There just isn't enough money in the system to support the 'proper' prices. So, for now they remain immensely profitable. Not enough people know about these stocks, or perhaps are concerned about putting their money in 'virtual' exchanges that theoretically give you no legal rights (according to the TOS)
I very strongly disagree with the argument that this has anything to do with how much money is around.
Half of the bitcoins that will ever exist have already been mined, I believe, leaving about 10M.
So, even if companies average 30% margin long term (I believe it will be much more competitive, 10-20%) it would only take ~3 million market cap across all companies to meet, if not exceed, fair value.
And very recently AM ALONE had a market cap of 2M at 5 BTC per share. So clearly there is plenty of money to get a company valued at whatever insane price you like, and it wouldn't take much to get it fairly valued either.
It is true that the market cap of something like Labcoin is very low, but they don't have a product yet. When it is clear which companies are going to be competitive, we will see reasonable valuation.
In the short-term, difficulty overshoot and negative profitability may kill some of the little guys, so that's yet another reason to be cautious with your money.