What would you say as the threshold as “serious net worth”?
1s, 10s, 100s of millions?
I think the issue is less the raw amount than the complexity of your assets.
If you just have a bunch of money... investing it on your own is still easy and cheap.
The complications come in when you have a complex set of assets (e.g., real estate, equity stakes in privately-held businesses, etc.) and income sources (salaries, proprietor's income, etc.).