Yes indeed @andr1an0, you are right.
I was rather thinking about the fact that if the price will rise along side with the exponential difficulty increase, ETH will still be profitable to mine until the last hard fork that will remove POW all together from the Ethereum Blockchain.
Lets say with 100 MH/s you currently farm 0.5 ETH / month. With ETH valued at 300 $ that would make a profit of 150 $ / month without counting electricity.

There are some other currencies, like Ubiq (UBQ) for example, currently at 2 $, that can earn better profits.
I am willing to research into such options and post my findings here so we can all benefit.