In an interview with Henry Oliver, Tyler Cowen tells an anecdote:

“I once had a conversation with a wealthy person, and he suggested to me the optimal level of wealth is $500 million. My guess, by the way is that he had about $500 million, which is not mega-wealthy. But I think he had quite a good argument. He pointed out, you’re not so so famous because of your wealth alone, like you may or may not have done something that’s renowned, your friends still might be your friends, you can manage the publicity, you probably don’t have to travel with security… There’s a lot of heterogeneity in human affiars, but I found that somewhat convincing. For me the number would be much lower than $500 million, I think it’s more like $50 million, in fact. But if you have $500 million, then you’re probably going to end up thinking you need $500 million to do all the things you want to do.”