Back to the question of choosing either a Mirror Universe or a Federation setting for Star Trek Online -- why not offer both?
Suppose ST:O created Mirror Universe locations and missions for those gamers whose primary interest is blowing stuff up, and (hmm -- what to call it?) Roddenberry's Universe for those gamers whose primary interest is cooperative exploration and socialization?
That doesn't imply that you couldn't do exploration/social stuff in the MU or combat in the RU -- the gameplay code might be the same for both places; only the rules of behavior would vary.
Don't think of it as "twice the work" -- think of it as "twice the opportunities." :)
