I love space, I love SpaceX in particular. That doesn't mean I think this valuation is out of whack. Facebook and Whatsapp have literally unprecedented reach. It's easy to hand wave off as 'just a messaging app', or 'just a social network', but we're talking about brands that achieved the global reach of Coca Cola in under 10 years. That's nothing to sneeze at.
Meanwhile, SpaceX is making something roughly as technically difficult as stuff Boeing, Lockheed, General Dynamics are all doing. Should those companies be worth more?
We continue to live in a strange time where people speak of "deserved" valuations without ever talking about future potential profits, both for space companies and even messaging apps.
Elsewhere in the comments, someone said that SpaceX will will simply "go public" to raise the money for Mars (sidenote: that must be an SV thing, to talk as if "going public" is like going to the ATM). Well, who in the public is going to invest without having some idea of what the business model here is, with a reasonable expectation of profits for the undertaken risk?
Look, I'm fascinated by the work SpaceX is doing too, but I need something more concrete than a bunch of loose ideas ("Mine asteroids! Launch satellites!") before I'd turn over my money. It will probably (hopefully) happen eventually, but until then any valuation is meaningless, high or low.
Edit: Seems like folks still like Uber around here. Use the taxi service at its current costs while you can; it's not gonna stay that way.