Jonah Goldberg of The Corner favors literacy tests, in principle. It's true that all votes aren't created equal. Some are more informed and reasoned than others. Why should the stupid majority tyrannize the intelligent minority? But who would concoct such a test, and who would determine what constitutes a passing grade?
Ah, there's the rub. You can be sure that the tests and standards would be jiggered to suit the party in power at the time they're established. And you can be sure that, once established, it would be difficult thereafter to change the tests and standards. There would be the usual "firestorm of controversy" and all that. So we'd be stuck with some combination of tests and standards that tends to exclude certain classes of people and skew election outcomes in the way that literacy tests and poll taxes did in the South for so many decades.
The real problem isn't that too many people vote. The real problem is that their elected representatives, in pandering for votes, have usurped powers that aren't rightly theirs. The solution, if one is ever to be found, lies in the proper interpretation of the Constitution by the Supreme Court. Making that happen should become a serious, long-term project of conservatives and libertarians, working together.
(There, I've re-established my credentials as a true libertarian by shooting down the idea of literacy tests. And I've suggested an alternative that ought to please libertarians. Please, may I have my "libertarian" card back?)