Impossible, right? Not really worth the time, right? Wrong on both accounts.

Many times while entering phrases into Google, I find a lot of somewhat related sites, but hardly ever anything exact. So why bother on getting these supposedly un-searched terms?

Because there is a perception that having your site in the #1 spot in Google means that your site is an authority on that particular subject. As any experienced user knows, this is most often not the case, but perception is reality.