On a small wiki analyzing web logs shows that 90% of the traffic
is search engines indexing the most useless places, like Allmessages,
old revisions, you name it. Every nook and cranny they've crawled
Therefore please increase nofollow links or whatever. Indeed, perhaps
just exclude all except current pages and categories, and keep them out of
Special: and Mediawiki: namespaces too, etc.
I see there is a $wgNamespaceRobotPolicies etc. but little wiki sysops
would not dare to tinker with these, so there should be better defaults.