The discounts are worrying.
That worries me as well, but I just bought a level 4 mine. That's not an amount of money that gives me a bad night of sleep when it's gone.
LOL.. same as you... invest in the amount you can afford to lose..
Lastly bitcoin price is getting exp... not an easy move now to buy it and invest as well and have to scare whether site will be gone or not.
Do not worry, you do not have to buy any new mines. It's not good to think about income too much. You can pay more attention to simple things in the life. Walking outside is one of them. It is free for anybody, but it is much more important than any business.
BTC is about $450 now and I believe that it will be much higher in next couple of years. So, from the other point of view, Bitcoin is cheap now.