I think it really will come down to if any of the classified documents were marked "classified" at the time. So far the only thing I've heard is the government (now) considers them too classified to reveal.
It's almost like someone telling you something and then after you reveal it to someone else they come back and say; "It's a secret".
If the information was not classified at the time will determine things.
Having said that I don't think Democrats care about this investigation at all! It seems only Hilary's rivals are concerned with this. The same holds true for Ted Cruz being born in Canada or Donald Trump having espoused non-conservative stances on abortion, healthcare, and befriending the Clintons.
Ultimately people are going to vote along party lines and for the people they like regardless of scandals, innuendos, or political flip flops. Both Democrats and Republicans are wasting their time trying to (choose) their opposition candidate to run against.
Donald Trump said he could shoot someone on 5th Ave and not lose his support! If Hilary Clinton does not win the Democrat nomination it won't be because of her emails or due to Republican wishes.
Bernie Sanders will have to defeat Clinton like Obama did.
The average person is more concerned with jobs, housing, healthcare, and taking care of their household.
This year especially it will take more than just "hating someone" or embroiling them in legal battles to defeat them.
One has to (win over voters) with their plans.