I'd like to give a giant +1 to Chris's suggestion - telling (potential) editors how many other people have read the article is a big motivator. It's logical really, we know this from the Education outreach projects and also from all the GLAM content donations: people REALLY are motivated by the fact that *their* writing and multimedia is being seen by lots of people.
Currently that information is rather hidden away in a link to the toolserver via the History tab. If you could bring that information more to the fore it could be really satisfying. For example:
"30 people have looked at your article since you made your edit." or, "350 people have seen this article in the last month" or even "6 other editors have changed this article and 500 people have read it since you last helped edit it". Perhaps you could even give some more complex breakdowns with pageviews by continent?
Just like making the timestamp more visible (and changing it to a relative number e.g. 6 hours since last edit), making the pageviews more visible are good ways of conveying the idea of how *immediate* and how *global* editing Wikipedia is.
-Liam