First, here are some queries asking how questions and answers score as a function of their lengths (in raw input characters, no sophisticated parsing here), with the associated graphs replicated here for convenience:
In both cases the mean score in each bin is shown together with +1-sigma and -1-sigma scores. There might be a slight upward trend for answers, but there is not really any trend to speak of for questions.
Perhaps a better measure is (score) / (page views). At least this way we are closer to answering the question "of those who looked at this question/answer, what fraction thought it was good?"
Voters don't seem to care much about a post's length.
Accepted vs. Not Accepted Answers
Could there be a difference in voting patterns as a function of post length between these two populations of answers?
It's a busy plot, but I don't see a trend in either population.
So, at least in this rough analysis, it seems post length really doesn't matter when it comes to votes. Of course, some of my answers I'm most proud of are rather long expositions on rich topics, so I'm not saying we should all write one-sentence answers to maximize votes per unit effort.
Finally, I leave this last graph that has nothing to do with post length. It's not really surprising; it shows that answer score is correlated with (the absolute value of) question score.