At this point, it's just ego.
It is almost entirely being spent or tied up in companies making and doing things.
It is not locked up in a Scrooge McDuck vault, or being used to build a gold monument somewhere
It's also worth noting that Elon isn't selling any stock in the IPO and has a one-year lockup to prevent any dumping. The main benefit to him is an enormous milestone-based comp package worth up to 750 billion if the company hits all the Milestones under his Direction. This is like the Tesla Milestone comp package that was so controversial, but I imagine that they closed the gaps. If they hit all the Milestones he deserves every penny. I think the most extreme one is a Mars colony with 1 million people.
People thought though Tesla compensation package was Pie in the Sky as well when it was granted, only complaining after it came true