Can the ELEMS be exchanged against NXT ? Also I don't understand the system of needing some NXT to mine ELEMS. Can you explain me ? If I could understand I could mine !
Registering your mined/minted ELEMS on the blockchain is a transaction and each transaction requires a fee to be paid (1 NXT) to prevent people spamming the blockchain and bloating it for free.
You can only swap/sell ELEMS for Nxt if there is buyer out there. So you should check how active the market is before you mine, if you are only looking to mine and dump. If you believe an MSCoin might have value in the future, for whatever reason, then you could just hold the MSCoin and wait until you are right.
I'm not part of those who mine and next sell it for some Bitcoins/USD. If I mine some ELEMS it's to keep ELEMS. But I don't like to mine something that has no value and cannot be exchanged for something that can be used to buy something.
If it were easy to tell if ELEMS will have any value in the future, then everyone would be here minting and filling their boots!

That's the risk/reward each person has to do. You might mine and only ever have sunk costs to show for it/
As crypto is so unpredictable, I might aim to mine a small percentage of as many MScoins as I can when they are easy to get up to a pocket change cost limit for each ($5-10) not expecting to get anything back for a long time, perhaps never on most of them.
Then all you need is to be holding 0.01% of the one that pops to make your money back and some profit. All the better if you can mine one that your can sell to cover your costs on the others.
But this still might be too high risk for many.