Two legitimate ideas surface from observation of ponzi scams. One is that there is no excuse for not being able to market to investors, if you are a semi-legitimate trader.
For example, these people manage to raise $100 mill+ in a year from dumb fish. Since there is no substance to their claims, this proves you can market anything to dumb fish, if you have flashy marketing. If you have semi-legitimate returns, you should simply copy ponzi marketing, and use the real returns. Just dress it up as some kind of "safe capital preservation fund" or something. Then put it in junk bonds, stocks, and Treasuries, and simply collect 2% management fees per annum with no risk whatsoever. You will probably actually make money for them too (and 100% more than they would make in a ponzi, lol).
Or simply trade the capital like a hedge fund. Voila, you just got a 100 m startup fund, with no performance record, investor interviews, nothing. You might even do well and make money for them and get rich legitimately!
Secondly, another business opportunity suggests itself. Why not hire private investigators to track down the operators of these scams before they get busted by the authorities. Unlike the authorities, you only need to find the people - you don't need to *prove* anything in a court.
Once you find them, simply hire a few heavies, go round, stick guns in their faces and tell them to pay you $10 million or you will kill them. What are they going to do, call the cops? Better still, these kind of scum *actually deserve to die*, so if they resist and you have to shoot them...well, you just did the world a service. Obviously, 99.9% of fraudsters will pay up 10% of the dough to save their skins, it's practically no risk.