effective altruism specifically encourages wealthy people to keep their wealth to themselves, so that they can use their billionaire galaxy brains to more effectively direct that capital towards long-term good.

And how is that a bad thing? The alternative is to spend money on stuff that doesn't work or even is actively harmful. The argument here is literally use less brain, do more pointless feelgood measures.

If, as they see it, Mars colonies tomorrow will help more people than healthcare or UBI or solar farms will today

Are we forgetting that Musk has an electric car company and used to have a solar company (since been absorbed into Tesla). He doesn't just want to go to Mars, he does a lot of other stuff as well. Also why should billionaires be responsible for UBI and healthcare? If Musk would spend all his money on healthcare, you'd have healthcare for about three months before he is bankrupt. That kind of stuff is the governments job.