I think we should do it, for no better reason than to remind us that we can do extraordinary things as a species. And I think the more we’re reminded of this, the more we might want to do other extraordinary things: cure cancer, feed the world, develop clean, cheap power. Which all require global, connected effort.
We’re always being told about the uplifting effects of global events, such as the Olympics- I think things like spaceflight can have the same consciousness-raising outcome.
Mind you, I’m not saying we should go to Mars first, but it should be on some list of things that humans should aspire to.