I was talking about this with a friend recently -- Romans flaunted their wealth by improving shared social infrastructure (open market spaces, parks, etc), and the robber barons of the 19th century flaunted their wealth by building cultural institutions (eg Carnegie libraries).

It seems like most "effective altruists" want to do things that help "humanity" but don't help "people" -- so developing technology to explore the stars is on the table, but fighting poverty is not.