You are assuming income and/or funds are linearly related to security under some definition of it. This is not necessarily true. It is correct that having more money gives you more ability to deal with potential threats to your security. In this way increasing money leads to increasing security. However, greater funds tend to attract greater threats and take more substantial effort to protect and maintain. This is why rich people do not lead completely stress free lives. There are more stressful and less stressful ways to make money, but I would suspect that if risk is proportional to income then it is impossible to eliminate some degree of stress from the act of increasing income.
It is possible that the particulars of the relations are such that up to a point, security benefits from extra money outweigh the cost incurred by having to manage those additional assets, after which increasing your money does not increase your happiness (limit of the difference is +0) or decreases it (e.g. happiness goes up with x^2 and stress cost with x^3). If so, it is possible that this point is $75k.
That suggests the question of boundless economical growth is at all possible, for example with corporations. Although huge, profitable corporations do exist, I think it is true that ultimately any market is finite- same as and because of the people on the planet, and the resources on it are finite, hence there is a diminishing returns acting on the agent. But is it possible that the diminishing returns become comprised largely of the security expenditures? Or, what about countries? Is there a fundamental limit to how large a state can becomes before it fails to maintain its own integrity, leading to eventual collapse?