Mene,
I stand to be corrected but with node wikis there are two ways to install plugins. One is via the file and plugins folder method. This can make plugins available to all node wikis under that server, however with a few exception dropping a plugin tiddler on a node wiki should install it in that wiki and operate for that wiki instance.
With a little work you can move whole wikis between node and single file wikis.
The people who use node/folder wikis a lot sometimes become quite node centred and and don't spell out the difference or assume node server knowledge (Not say that what Mark has done).
I see quite a bit of chatter here based on this node/folder vs Single File wikis that leads to confusion and questions.
Regards
Tony