I can answer some of your questions. The longevity and age of onset of patients with familial ALS is partially dependent on the mutation they harbor. That being said, genetic background is an important contributor. Fortunately or unfortunately, familial ALS isn't common enough to have significant statistics on the matter. To my knowledge there is no solid proof that environmental factors play a role in ALS. I'm fairly certain some will be discovered, but to date specific factors that enhance or prevent ALS are not known. On the issue of veterans, it is thought that the enhanced physical activity may be the cause for the increased risk of ALS, though the increase is merely 2 fold and once again the statistics are poor. If I remember correctly, this increased risk was present for both combat veterans and those that didn't see any combat. Once again outcomes are identical with the civilian population.

I don't believe that his longevity decreases the urgency for research into the matter. However, compared with disorders such as Alzheimer's disease, cancer, and heart disease, which combined will affect some large percentage of the population, the 1:1000 lifetime risk for ALS makes it somewhat insignificant.