Aaron Wall has a good post which discusses the effects of top rankings for low return keywords. Rankings for non-performing keywords chokes you with low quality traffic. What if someone else pushes you into the front ranks for such keywords? Aaron posts quite a few ways of reciprocating the favor, such as:
Alter the topic of the page?
Remove the page from your site if it was of low value?
Change the purpose of the page to harvest and distribute link equity?
Point a few links at authoritative websites (like newspapers)?
Edit the Wikipedia to put a few extra words in an article?
I am a little doubtful about the effectivity of the last one though. Wikipedia has stopped being a ground for such rivalries with stricter editorial supervision. Wikipedia doesn't really have the power of sanction that the Digg community often practices. But you would be safer not to ignore it altogether too.