To me, this feature is more useful as a voting system, in the "I want to add this feature" and "Get rid of this feature boards".It's usefulness as a rating system, trying to rate which topics are "more important" or "more worthwhile" is a dicey veture at best. The obvious problem you have pointed out is that it doesn't really say what criteria we are using to "rate" things.
The exception to this might be the "About this Board" board - most people would probably agree on what was "important" reading there (all of it, of course ).
I think (at least to me) that the ratings in the rest of the boards, should try an indicate whether you felt it was worth your time to read the topic or not. That way (and this is how I have viewed the numbers so far) the rating can help point out the more interesting or informative topics. Like you, I read every one of them anyways, but I do keep an eye on the ratings. I figure if someone took the extra time to rate a topic, that counts for something.