Thanks a lot for all your responses and links for further reading!
The problem is that in my current position (technically I'm just an intern), I have no way of handing out motivators of any kind - let alone making use mandatory. Even getting everyone to just enter their name and position (to make them take a look at the wiki) is quite a challenge... And the project leader wouldn't be willing to take any such steps before he sees that the wiki is actually working - kind of a catch-22...
I will get the chance to make a (very brief) presentation though. Obviously I'll have to make a good case for the wiki there (not one of my best qualities) in order to get people to at least consider using it. So as of now, I'm hoping for a "cascade effect" where a few eager colleagues will pick it up, and then others might follow. (I will of course be present to answer whatever questions might arise.)
As for a WYSIWYG interface, I'd agree that while this might erase the intial obstacle, its (current?) limitations would likely lead to frustration further down the line. I'd consider WYSIWYG if advanced users could just turn it off, but it seems that all available solutions/extensions change the way contents are saved, creating an either/or situation. (This might also lead to complications when trying to export contents from the wiki for use in some other medium!?)
Thanks again for you kind and truly helpful contributions!
-- Frederik