In the short run, the dozens of urban riots in the 60's won some reforms in the War on Poverty and Great Society. In the long run, it motivated the Nixon Southern Strategy and the Reaganites, who have come to dominate the US polity; and they r steadily reversing the 60's reforms and even the 30's reforms.
I think strict non-violence , which includes peaceful civil disobedience, should be the Occupy tactic. This will influence mass voting in our favor.
I don't disagree that the police are the main violent actors in the Occupation context. Strictly speaking vandalism is not violence, because violence is force used against humans, not material objects. However, I think the fundamental problem with BB's and anarchists' strategy is that it is not to make reforms through voting, so the tactics are not aimed at influencing votes.
Charles