[abraxas]

This was solved in 1995 with WikiWikiWeb. Not sure why the bi directional links did not become more of a standard.

[webmaven]

Bi-directional links basically leads to linkspam of various sorts. Aside from actual spam, you get the pages that are popular link targets having ginormous lists of backlinks to too many other pages in the wiki (which makes the backlink list useless).

Better to have specialized templates and page types to expose the right amount of context (eg. Wikipedia category pages, navboxes, sidebars, etc.).