There is actually visual feedback after upvoting already :
When a story is upvoted, only the 'up' arrow will remain displayed, and the 'down' arrow will be hidden. When a story is downvoted, it's the other way around.
There has been a pull request on this topic : https://github.com/antirez/lamernews/pull/121
So maybe the issue should be reopened, if more people think it's a good idea?