"Then he must be bad at business" is a weak line of argument, because he is clearly worth a lot today. You are asking people to ignore the tangible evidence of today in favor of some incomplete information from two decades ago.
I'm not sure where so-called moderates fall on the question of fairness over not paying taxes. Warren Buffett has become something of a hero of the left for arguing that billionaires should pay more in taxes. When Republicans ask why he doesn't just choose to pay more, he says that it is his job to take advantage of the laws on the books, and that the solution is to change the laws, not to expect billionaires to pay more than they are required to. It is the exact same argument with Trump. My intuition is that a lot of people do think it's smart to avoid taxes when you can do so legally, because Americans in general tend to lean more toward individualism than collectivism. So I am skeptical that this line of attack will do much damage among voters either, aside from maybe energizing Clinton supporters a little more.
I suspect that the real damage from the story will be less about the actual facts, and more about keeping Trump on the defensive (since he is prone to doing stupid stuff in that situation) and to keep the doubts about what else might be in the taxes in the news - sort of analogous to the attacks on the Clinton Foundation.