My feeling is that this is a problem that is only going to continue to grow as more and more people start using Waze -
imho, the way to deal with this kind of problem is to introduce a more restricted editor permission structure. It probably goes against the original waze culture.
Another problem i've noticed (is it a problem?) is some users deleting and re-creating well-established roads, i can only assume to gain points for what it's worth...
and yes, there's the good old 'edit the map to match the aerial imagery' muppets