Sorry for the long response!
I took nothing personally, Little Joe. The difference is that a "poll tax" simply enables folks with money to vote at the expense of those without money. Having money is not a prerequisite for being able to be a responsible voter. So, no, I do not believe a poll tax is an answer.
As for a comptency test, I would merely point out that most democracies, with absolutely no right ennunciated in their constitutions to do so, nevertheless divine a right to regulate their populations rights to drive, own weapons, etc. A test is usually involved. That also could be construed simply as a test of the educational system. It is in reality an attempt to make sure you don't accidentally hurt anyone else while driving or using your firearms.
So, back to voting. Not having any knowledge of what's going on, or what the consequences of your vote might be can and will also lead to the injury of others, can it not? I share everyone else's ingrained belief that "one man one vote" is the way it ought to be. But what I am asking, is why? I feel it rather than logically know it. A voting comptenecy test could be as simple as, "Do you know your own name? Can you spell it? What's the name of this country?" if you just want to be sure that a voter is mentally competent to the responsibility, ranging up to much more if you really wanted a "driver's license", "weapon's license" type test.
Doing so may mean that your country isn't a true representative democracy anymore, I don't know. You might even call it a democratic dictatorship in that only those who have proven able, choose those who will lead.
BUT consider this: Not having the right to vote without earning it might just be the impetus for all those who know nothing to get the knowledge they need to earn their voting rights. No one would be keeping anyone from doing that, and in fact this would be a huge incentive to do just that and allow democracy to flourish!
Food for thought.