I think I get it;
1)Using Group I can make a specific part of a single wiki page invisible to the unwashed (in your case a link, though I've used it mostly for text).
2)I can protect pages by assigning permissions to a page but then I have to laboriously assign group permissions for every page.
3)You are going one step farther to save the trouble of assigning permissions for every page by just assigning them a category (am I getting this use of categories here?)
4)You are wanting to go a second step father and ask the question "If the pages are protected from view why show the link at all? Especially if that link's name might actually expose information. Since Tiki can hide modules, why not links?
5) These links, then would be dynamically hidden anywhere else they appeared in the wiki. Kind of like assigning permissions to a page link.
At this point you can see I am obviously way out of my league here!