1) Most 16-year-olds won't vote anyway; only the super-motivated and exceptionally intelligent will care enough. Hell, hardly any 18-year-olds vote, and I think a majority of the voting-eligible public fails to vote even for presidential elections.
2) Even if they did vote en masse, they'd be a miniscule bloc, and one that candidates would lose more votes than they'd gain by pandering to. Or perhaps they could help a third-party candidate gain more than .7% of the vote.
3) Allowing 16-year-olds to vote will get people thinking about the issues at a younger age, which is good for any country.
The only danger I see is 16-year-olds becoming tools of their parents: "You vote for X or you're grounded!" Of course secret ballot kind of takes the teeth out of that one.