Then people could turn on or off some way to see which posts are heavily agreed or disagreed with without downvoting interesting posts just because you disagree. You could even have a system where you mark people you respect and then only see which posts they agreed with to get a more personal feel? Might be an interesting discussion board idea to pursue.
There are several factors that ensure better Signal to Noise ratios in communities.
Protective Moats, specific technical subject matter, for example.
Essentially it boils down to difficulty to engage, or non trivial effort required to engage.
The factors you mentioned have little impact on the behavior of the sub, which is mostly influenced by the people and norms of behavior, over the UI.