First, you have no idea what the difficulty will do, none of us do. Secondly, even if the higher price of BTC does drive some larger difficulty increases, it also offsets your electricity cost. Third, when you bought the miner you surely did a model on how long it would take to ROI, and whether it was a good investment at the time or not (in BTC) regardless of the future price of BTC. Higher BTC price just means you will ROI faster due to lower costs, so stop complaining about it. If only we would have all bought bitcoin in 2012 too.
As for solo mining, here is my thought on it (note: difficulty has increased since I posted this, so odds are slightly lower):
More realistically than trying to anticipate a time frame to find a block (because by nature that is impossible due to probability), is to look at every block that's found.
At this moment, with 10 TH/s you have approximately a 1 in 46,338 chance of holding the magic hash every time a block is found. Those odds do not lower at every block as the calculators would have you believe, they are the same odds every time (until difficulty is adjusted, and personally I would plan for a ~3% average difficulty increase between now and the halving)
You could have a 1 MH/s miner and the first hash that goes out is the winner, or likewise you could have 1 PH/s and go weeks without a block. Do yourself a favour and look at some of the medium-sized pools (like Eligius for example) and look at the block history and their luck. The variance is huge, and they are operating with 14 PH/s. For you to solve 1 block within 300 days would require flat difficulty and >100% luck in comparison. Imagine how it would play out if "your" block was a 25% luck block (you would have to mine for ~3.25 years with your hashrate keeping up with difficulty if that was the case).
I hope this makes sense.
