In the 1800's, education levels were generally low. I think it's safe to say that less than 10% of people graduated from high school (although education wasn't a high enough priority to keep statistics on in the 1800's, so it would be tough to verify that statement). Voter turnout was in the 70% to 80% range.
By 1940, 40% of kids graduated from high school. That still meant that over 70% of the population hadn't graduated from high school, since the emphasis on education was so recent (the first year that education levels were a high enough priority to be included in the census). Now, over 85% of the population are high school graduates. Voter turnout has ranged from 50% to 60% for most of the 20th century and later.
http://en.wikipedia.org/wiki/Voter_t...tial_elections
http://www.census.gov/hhes/socdemo/e...rical/fig2.jpg
So associating higher education levels with voter responsibility may not be valid. It would be equally invalid to say higher education levels decrease voter responsibility.
It's more likely lower voter turnouts and higher education levels had a common cause, though. Increased urbanization requires higher education levels, but it also leaves the average person feeling less connected to his government and what the government does.
In a small town, a person might be pretty darn sure they don't want to vote Barney Fife for sheriff because they're afraid to let him carry a gun. In a large metropolis, the average voter doesn't really know the people he's voting for. He's relying on what other people say about him (and doesn't really know the people he's listening to, for that matter).
The disconnect between the average person and people in government bothers people regardless of their education level, but the response to that disconnect could be related to education level. That disconnect is part of the reason the idea of term limits are so popular and why even a city of 400,000 might only pay its city council members $7,000 a year. They don't like the idea of full time politicians that respond more to special interest groups padding their wallets than they do to voters. But it also glosses over the fact that policies like these tend to guarantee that their government will be run by amateurs with none to little experience running a city or state (and that's a naivity that could certainly be related to education level).
But, in general, I think you're attacking the wrong problem by focusing on education levels (but at least you only seem to be disenfranchising 30% of the population since half the people don't vote, anyway).