I make over 3x that much now, and I wouldn't say my financial happiness is much greater. The marginal utility/happiness of getting a 2nd vehicle is tiny compared to going from 0 cars to 1 car.
I've been thinking the same thing for years. I said to a friend once that the more you make, the less happiness payoff you get.
The guy living on the street who gets a job which can pay for a furnished room has just increased his happiness tremendously, because now he doesn't have to get wet when it rains, he doesn't freeze when it gets cold, and he doesn't have to go find a place to go to the bathroom. That's a huge difference.
When he gets a slightly better job and can afford a used car, his happiness increases quite a bit, but not as much. Being able to get around to places without having to walk there is wonderful, but not quite as wonderful as getting off the street and getting warm.
When he gets his own apartment and doesn't have to share kitchen and bathroom facilities with other tenants, that's also a big step up, but again not as much. And so on for getting your own house, getting a second vacation home, etc.
By the time it gets to where you own your own house and a summer house, plus investment to keep it all going, you approach zero increase in happiness when you can afford to buy more houses. Although I don't think you ever hit negative territory.
I tried explaining this to a friend once and he looked at me like he's waiting for the Nice Men In The White Coats to pick me up any moment. So you might run into the same reaction here.