I really don't understand folk's obsession with someones wealth or what taxes have been paid. It's obvious Trump is a millionaire, so what? And if he managed to take advantage of the Congresses tax monstrosity and paid zero taxes he is the best candidate as far as smarts goes. It would be really great if he managed to even get a tax credit refund!
He's trying to become the President of the United States. He is proposing tax policy. By seeing his taxes we could get a glimpse of how he handles his own taxes. This would be a good clue as to how he would handle tax issues for the rest of the nation.
It would take a lot of explaining, all of it in vain I'm afraid, for Trump to convince the average American why it was a good thing that he made $600 million last year and paid no taxes.
His tax returns would also give us an idea of how charitable he is and what charities are important to him.
BTW, he's already said he would not put his assets in a blind trust, but would have his children actively manage his businesses. That is a recipe for a conflict of interest.