Having built a lot of plugins for fun and for hire, I would highly suggest sticking to topics. If you vote on posts, the next natural question is: how do you view posts in rank order?
That dictates a need to reorder a stream of posts. Having done that once (and once was all it took), you’ll need to set aside a hefty budget to commission it.
If at all possible, I would look for a way to set up multiple categories within a parent Nominations category.