What is the effect of high expectations on long-term happiness? Are there any studies about the long term effects of having high expectations of oneself on one's happiness? Does crashing after failing to reach unrealistic goals significantly impact long-term happiness?
There are definitely studies on this, but I don't have the references at hand. I've heard about this in the online Harvard courses on positive psychology by Tal Ben-Shahar.

In terms of "crashing", there are studies about baseline-happiness, showing you bounce back up after a setback, and back down, after a positive event, like winning the lottery. Only intrinsic perspective changes can increase or decrease your base-level of happiness.

He also talks about a study showing "pessimists" are better at estimating their short and long term success rate. And "optimists" are bad at estimating short term, but good at estimating long term success. The interesting thing is, the pessimists set lower expectations, and their base-level of happiness remains. The optimists have higher expectations, and try until they succeed. The increased belief in their own efficacy, and resilience in the face of a set back, helps to increase their base-level of happiness.

On the other side of the coin, he stresses the importance of "realistic optimism". He says the keys to success are a combination of optimism, passion and hard work. Only optimism (high expectations) is not enough. A quote, by approximation, by Maslow: 


  Too much optimism does not lead to success, and results in depression. A sense of reality is needed.


You can look into the Stockdale paradox.

Sorry I can't give you a shorter, more concise answer at the moment, maybe I'll revisit this later.