I think both comments and posts should be evaluated (separately), but i agree that voting patterns are very different.

Regarding how long it'd take, that depends to strength of the effect... what i think is the strongest effect, is that anything negative gets read much more critically - where a + voted post's assertions will get read and seen in positive light if at all plausible, negative-voted assertions are likely to be immediately challenged (do they compel me to believe style) - it should be general reflex, that's just being a good Bayesian reasoner, but it leads to circular reasoning problems when everyone's reasoning this way together.

If I were to have a theory that you guys tend to apply bayesian reasoning in practice when reading posts, the vote spiral would follow as a testable hypothesis. It's just how that stuff works in networks. Bayesian reasoning requires tracking where the data is originating from.