I tend to agree with j-e-f-f-e-r-s. Even the least-informed can form positions, at least as basic as "I want the government to take as little of the money I earn as possible; each person is entitled to the fruits of his own labors, and the government should take only a portion for essential public services" or "I want the government to take money earned by others and give it to me; a disparity in wealth hurts a society and is unfair." Certainly you can argue such simplistic concepts don't make for the best results for the country as a whole, but any group in control of who is eligible for voting will make that determination based on their own self-interests. And don't forget that highly educated, knowledgeable people argue those same two simplistic concepts every day in politics. Even if the prospective voter holds such simplistic political views as those I mentioned, we still don't have determination of which theory is correct. I could easily make a cogent argument for either.
There were reasons originally to limit voting to rich white landowners, and you can argue they did an excellent job for the most part for the country as a whole - but they ran the country for the benefit of rich white landowners. If you were a poor black sharecropper (or slave) during the same period of time, I'm guessing you'd prefer a say in how the country is governed to a larger increase in GDP. Past the first generation, a group in power will always govern in its own perceived best interests. Similarly, I believe that any attempt to limit the number of people enfranchised will always be twisted to the benefit of those in charge.
(Sorry for the spelling, I'm typing on my new computer and I don't yet have anything with spell-check loaded.)