This is actually what we did with the Midgard wiki for a while, but there are two big problems. First, the old wiki will clutter up Google searches (this was a bigger problem with the Midgard wiki which had a high page rank, but still) with old pages filled with old information. Second, an uneditable wiki is a really unproductive oxy***** because people frequently don't see the notice, want to update these old pages, and don't understand that there are newer, more up-to-date and editable pages available.

It really didn't work very well. Better to salvage what's usable and kill the rest. The salvage part has been done (AndrewFBlack moved the pages, and I did some merging, cleanup and deletion). You could certainly argue that the threshold for quality was set too high or that the article selection was too . . . selective, but it's done with now.

In summary, if you run into something that's missing or needs expansion, mention it and somebody will get around to putting their knowledge down in the wiki soon enough.