The problem is with cryptocoins, the window of opportunity is always small, short, and never comes again- you have to find an entirely new window.

Much like with most forms of arbitrage, and exploitable patterns in the stock market. You discovery the opportunity, you make a little $$, and the hole quickly closes as everyone else capitalizes on it too.

I don't think it would, actually. Enough people are willing to mine for a loss and the difficulty rises with availability of cheap hardware that it never becomes profitable. OP only made a (slight) profit because they could temporarily make renting a miner cheaper than the payout. This was temporary and now the market is back to status quo.

Maybe OP could automatically run his miners when such situations arrive, but I think it's unlikely to net anything like $17k/yr.

Edit: sliverstorm described this way better than I could.