I think user rank and the decrease in vote power was supposed to fulfill that function in a mechanical way (without allowing gaming of the system). Somehow, that has either been broken or is not functioning as well as it could.

A possible adjustment along your lines could be a (or 2 kinds of votes) a "standard" upvote (unlimited) and a "money" upvote, of which you get 5 a day, on a recharging basis. (I essentially wonder if people are not voting enough for the curate function to work). This way you get 2 dimensions: popular posts and valuable posts.