Appoint a chief editor. Chief's most important job would be to maintain a list of what most urgently needs adding or expanding in the wiki, and posting a monthly Discussion post reminding people about these. (Maybe choosing a different theme each month and listing a few requested edits in that category, together with a link to the wiki page that contains the full list).

When people make these changes, they can add a comment and chief editor (or some other high status figure) will respond with heaps of praise.

People will naturally bring up any other topics they'd like to see on the wiki or general comments about the wiki. Chief editor should take account of these and where relevant bring them up with the relevant people (e.g. the programmers).