An interview I recently read with Seth Rogen was very illuminating (from the NY Times):

"You know how every once in a while you read one sentence and it snaps your whole perspective into place? I remember reading that book “Going Clear,” about Scientology, and there was one sentence about how if famous people aren’t treated in a certain way, it makes them think they’re not as talented as they wish they were. Like, if I go to a restaurant and I have to wait 20 minutes for a table instead of them just seating me right away, am I not as talented as I thought I was? If someone has a nicer hotel room than me on the press tour, does that mean I’m not as good an actor as I thought I was? I think that’s how a lot of famous people interpret how they’re treated."

I think the same applies to Musk. The money is a proxy for how much everybody thinks he is a special genius. Anything in his life that makes him feel less special requires more validation that he is, and money is the easiest validation he is able to acquire.