The decision on whether to buy coins directly or invest in a mining rig depends on the current market (price of bitcoin and difficulty factor) relative to future change. When bitcoins are cheap buy bitcoins. When bitcoins are expensive buy rigs. To spread the risk in the face of uncertainty, go half and half.
The profit from mining is there, but at this junction just buying may be more profitable without the hassles of buying and selling equipment at the right time and suffering with heat and other issues maintaining a mining operation. I didn't recognize that I fell in this category about 3 months back and now although I am about to recover my cost, my pure profit run won't last long as I hoped at all. Now I'm considering selling my setup in a month or two depending on and then just investing the money. In fact I actually saw few ads of people selling rigs already.
This is the reality for me at least. I could have made even more money just buying outright and have more coins and more money in my pocket with nothing to sell this very day. But this is looking in hindsight after seeing the price jump from .7 to 4. about 5 fold increase. People are asking these questions because they are smart and when people give them answers other than blindly mine, others second guess their intentions. Say what you will, I don't regret going into mining at all, but I do wish that I just bought the btc when it was cheap because I would have ended up with more today.
If you bought a rig instead of coins when coins were cheap, and their price rose over a short period, then you missed profit over that short-term, sure. In reaction, let's say you now decide to sell your rig and buy coins. But now you might be buying coins when they are expensive, and their price may not rise over the next short-term. So this term your profits could be zero or negative. You might have more coins but your only chance of profit is speculation. If you keep the rig you would be earning coins consistently.
50 days is almost enough time for 5 difficulty increases. The next one is already projected to be over 30%.
If this increase is 30%, and the next increase is 30%, etc. Then after 5 difficulty increases of 30% you'll be making a bit more than 25% of what you're seeing now.
Take the difficulty increases into account, run your projection in a spreadsheet by difficulty periods (about 10-11 days each) and then calculate your payoff.
Any mining profitability calculations beyond a few does absolutely must take rising difficulty into account.
You're estimating the payoff by projecting an increase in difficulty, but assuming a stagnant price. This makes no sense. In order to estimate your payoff you have to predict the future price of bitcoin, which is highly volatile.
There's also no rule that says the difficulty consistently increases. Actually, we have seen the difficulty drop when price drops.
Whether you mine coin or whether you buy coin, both can be equally profitable. The trick is selling high (after mining cheap and holding, or buying low and holding).