Given, as I pointed out earlier, the tax take from the well-off and wealthy has dropped substantially over the last few decades as taxation has shifted from wealth and assets to income, the idea we can make it up by scrounging up some money from the cash economy is simply laughable.
The 75% rate doesn't kick in until a taxable income of ~1.25 million USD. I might just have to dig up my tiny violin and play a song.
The countries of Northern Europe demonstrate quite handily it's possible to have tax rates much higher than ours, while maintaining vibrant, innovative, entrepreneurial economies and the highest livings standards and levels of equality in the world.
America demonstrates what happens when you follow the neoliberal religion of "taxes are always too high and must be reduced", "worship the rich" and "blame the poor for everything".