There should be two separate votes

As it is, people simply misuse the voting system. Despite the guideline's clear explanation that they are not to be used to show agreement, that's how they're used.

Instead, there should be two votes. One to show agreement, and the other to show if you thought the thread was good for discussion.

Of course, there will still be the a-holes who just click down on both of them because they disagree, but my hope is that there will be enough people using it right to offset that.