There have been many examples in History of various types of census for voters. The examples would include land ownership, income, age, gender, race, literacy, etc. Many of those have been detrimental to democracy, but is that true for all kinds of census?
A discussion appeared in the comments to another question whether it would be beneficial to have basic literacy + numeracy test for prospective voters.
Pro: The voice of reasonable people often drowns in the noise of unreasonable ones; restricting voting to those who can critically understand politicians' arguments and have basic understanding of economics and statistics may lead to better government. Voting in USA often includes direct democracy, such as voting for propositions in California and other states. Literacy level of voters may have direct effect on the laws. We already have written test for obtaining a driver's license because driving a motor vehicle implies responsibility. Why should we require less responsibility in development of the laws we live by?
Con: There has been a history in USA of using literacy tests to disenfranchise a part of the population. Wouldn't less literate portion of the population get disenfranchised again?