Musk, Mars and x-risk

Ar­ti­cle on

Elon Musk, the billion­aire founder and CEO of the pri­vate spaceflight com­pany SpaceX, wants to help es­tab­lish a Mars colony of up to 80,000 peo­ple by fer­ry­ing ex­plor­ers to the Red Planet for per­haps $500,000 a trip.

Rele­vant Sa­gan quote:
(...) we’ve put all our eggs in one bas­ket. If we were on many wor­lds and were to mess up down here, there’s a way for the hu­man species to con­tinue. I don’t for a mo­ment pro­pose that the Earth is a dis­pos­able planet, and we have to put enor­mous efforts into mak­ing sure we don’t muss up down here. But there is a chance.
This should also at least some­what re­duce the x-risk stem­ming from uFAI (a sub­set of uFAI’s may not con­cern them­selves with space travel), and may sig­nifi­cantly re­duce the x-risk posed by many other x-risk cat­e­gories (bio­eng­ineered threats, catas­trophic cli­mate change, global nu­clear catas­tro­phe, grey goo sce­nar­ios, etcetera).
For to­tal x-risk re­duc­tion, prima fa­cie it’s un­clear to me how sup­port­ing an en­deavor such as Musk’s stacks up against the SI’s effec­tive­ness, mea­sured by to­tal x-risk re­duc­tion per donated cur­rency unit.
What’s your take?