I think Bill Gates has the best plan for the wealthy. Targeting specific problems (Polio, Malaria etc.), solving them, and vastly (and quickly) improving people's lives with the aim of bringing people out of poverty.
I don't deny Musk could do fantastic things with that money that would benefit some of humanity but it seems more important to me that we get those in poverty out of it. That's more important for humanity than building the hyperloop or going to Mars. For even the middle classes life is pretty good. Get everyone up to that level.
The poor I'm talking about are people who have insufficient food and fresh water. You can't expect people to pull themselves up by their own bootstraps when they're dying of malnutrition and disease in the middle of a country with a dysfunctional government.