Well maybe I mis-read you, but you stated, "I would be inclined to set a flat, top limit of personal/family worth ..."
When you write worth, do you mean total wealth, or amount earned through salary per year? I define worth as the former, which if you set a limit on becomes a detriment to the economy. Taxing only earnings, and not wealth, is not part of the Democrat platform right now, which I why I jumped right to wealth.
Insofar as taxing the rich at higher and higher rates opens the door for more and more kickbacks. You really think that making the tax system more complicated wont bring more cronyism and will make things fairer? That's not how things work out.
The answer to your question is the first: total wealth that is not
invested in some part of your own or other businesses. Earn whatever you can, but make sure you reinvest. As they say, money lying in the bank is a stinking fish. Having fifty million squids in you bank is stink quite enough, I'd have thought.
Again, you are writing in terms of taxing the rich more and more. That is not what I am suggesting. I am suggesting they be forced to reinvest or, if they refuse, then tax the knickers off 'em. They obviously have no need for it and so yeah, spread it around to help other businesses get going.
It has been my belief that only being self-employed for at least a year will be enough to teach one that the world owes nobody a living. Knowing that, and understanding how too low a starting capital can hinder your growth (see Slobodan's point about Musk and my reply to that), it comes as no surprise that the looney left thinks that business owners have it easy: nobody does, and it's always a battle to stay put, never mind grow. That's one of the prime reasons for "encouraging" the über rich to keep their pennies working either in their own companies or in others. I don't think of bank accounts as being your money working. More, it pays bankers a pile and stays out of the hands of those wanting business loans but refused them for being too modest. Frankly, I think it is part and parcel of the death of the local shop: you don't want to do everything online - I would do
nothing online if a real shop was still around. It's some of those amazing inventions and innovations of the globals that are actually killing us off as little people in business. Thinking of them as some kind of benefactor is back to turkeys and X'mas. It won't do simply to suggest that the small guy get smart; if he can keep himself and family living reasonably well, good enough. Not everyone is driven to obsessive lengths over something, or even has both the acumen and luck to make it thrive. But hey, one little family tending their little store is better, in my eyes, than one more blue-collar job hoping to outlast the march of the robots in the factory.