Everybody should vote. If you feel that you don't know enough it is always possible to vote blank. Making it legitimate not to vote (as it seems to be is some circles in USA) is to make it legitimate not to participate in the democracy. The low turnout is a serious problem and any acceptance of limiting access to voting or encourage people not to vote because of any reason is a threat to democracy
NO. Not everybody should vote. One of the problems with democracy, and voting in general, is that the vote of a complete moron is of exact equal value to the vote of an intelligent individual. Guess which one is more likely to screw up the system if he votes? And let me tell you, the apathetic, the stupid, and the ignorant far outnumber the knowledgeable and intelligent. But the apathetic, stupid, and ignorant are less likely to vote than those who actually know what they are doing, so that makes the intelligent vote more valuable and effective.
The greatest argument against democracy is a conversation with the average voter.
As you probably would guess I disagree (and that sentense is one of Churchills. He never liked democracy that much, mostly because the voters wouldn't do as he said). You don't sound like a supporter of democracy "the lesser of the bads" more like a supporter of Oligacy.
The basic idea is "one person, one vote." You might disagree with the motivations of some voters (fx: "X has a nicer wife, that is why I vote for him") but that does not invalidate their choises. Many countries have had high turnouts for decades (Denmark, Sweden and Norway between 80 and 90% the last 50 years) without hordes of "stupid" voters following the first the best demagog. Limiting the voting rights is the first step on the road to dictatorship and frankly I am quite surprised that a Libertarian would support such a thing