I recently read Eat & Run from Scott Jurek and Ultra Marathon Man from Dean Karnazes. Both stories are very inspiring and strengthen my feeling that I have to try a 50 miles. Also, the book from Karnazes raised the question about the reason of running. While each of us has a different reason and, when going for crazy distance, a real inspiring story, I would like to take advantage of my efforts to help other people.
In that context, the story from Dean makes sense. The guy runs to raise money and help children having health disease. It helped children have treatment for heart or lung disease. While you can keep your own motivation, running for charity would be a nice gift you can do for somebody else.
In the light of an on-going mid-life crisis, running for somebody, help other people is something motivating. Something to consider, running is a way to connect with nature, if it can be also a way to connect with other people, especially non-runners or people in needs, it will just make the journey definitively worth it.