it's all about electricity, if you have very cheap one like 0.03 or 0.01 like in kuwait, you can basically keep mining forever, there is no dead times for you in that case

even if your single gpu do only $10 per month, with 100 of them you could make it like a full time job, but only with insignificant electricity cost

If there is active development of the Ethereum and the price will rise slowly to adjust to the value.

It's very difficult for a non miner to make a guess about the real value of 1BTC, but it depends on the pool that mines a block. If it takes them 3 hours to mine a block, then all costs made during these 3 hours will be divided by 25, and that will for that pool be the real price.

Price won't be stable soon, now it's 398$ but  i think that their price will rise to 600$or even more by the end of 2016

What people also tend to forget is that the mining will stop this summer for Ethereum, so this is obvious that this contract will never be profitable.