One interesting Wikimania session by Seth Anthony presented some research on contribution patterns. My notes:
Only 10% of edits are high content edits. 30% of those are anonymous, none are by admins, 52% are by someone with a userpage, none have a barnstar. The people who are creating content are relatively new, not versed in style guides and bureaucracy. Their use of Wikipedia speeds up a little bit through use, but not much.
Admins, on the other hand, are relatively efficient in their edits and have a consistent pace. They only edit within the article namespace 60% of the time. In other words, most edits are revisions of vandalism. But in the early days they edited less frequently, created more content (76% of the time) and edited less consistently.
Content creators seem to be occasional and less frequent editors that may be specialists (subject matter knowledge). Admins are former content creators, now janitors. One person in the audience volunteered that he just crossed over from subject expert to janitor to emphasize this point.
In other words, the core community within the Power Law of Participation, the 500 people that do 50% of the edits, or 0.5% of the registered population -- does the heavy lifting for subject experts. Advances like Wikiwyg may increase the number and diversity of subject expert contributors. With 2 million edits per month and vandalism anecdotally scaling linearly with edits, janitors matter. Recruiting core community members (not sure if his research showed the rate of conversion) and scaling the core in a non-bureaucratic way will be necessary for fulfilling goals for enhancing quality as well.
I should highlight, as with most things, Wikipedia is an exception for wiki communities. Their committment to giving Permission to Participate results in a higher burden than most communities carry. But even in an enterprise community, a core needs to arise to carry what some people would consider a burden. Gardeners don't spend time killing varmints, but instead prune the information architecture and watering areas for growth. As a result, I'd wager that the percentage of high content edits is significantly greater.