The slider is an interesting notion. It adds user-interface complexity, and may have incentive problems for users who desire to exert control, but potentially garners a substantially more useful form of information.
The problem of the desire to exert control makes me think that a better option is giving a limited number of double/super/special votes that users can ration out as they see fit. Extra votes that actually mean something.
Here is our monthly place to discuss Less Wrong topics that have not appeared in recent posts.