Wikicup is highly structured and targeted towards improving quality and attracts only a small number of participants. It appears to be targeting existing editors to make better quality contributions. So it’s certainly an example of gamification, but not one that’s likely to find “mass appeal” or attract/motivate new editors.
I think if we are looking for “mass appeal” then I think we need to look at “casual gaming” and what makes them tick. Why do people play little short-play games? What’s the equivalent for Wikipedia? Could we create a “game” that throws up a random “citation needed” (perhaps in a particular category) and asks for a URL that supports the claim? The game would have to have other “players” checking the citation or else people would upload any old URL. Maybe it could be structured along the lines of Yahoo Answers, where the “players” get Best Answer statistics and can be on leaderboards for different categories of content. There’s a nice match here to Wikipedia since we already have categories.