I'm all for stories having an ending. Even Galactica, despite only being around three seasons, had more than its fair share of "treading water" episodes where it feels like they're just killing time. By giving it a focused pace which is building towards something, it'll help the storytelling a lot.
Otherwise, this'll be the X-Files all over again... monumental story shifts and developments that never actually go anywhere, become far too complicated for their own good, and eventually collapse when an ending is forced on it due to sinking ratings rather than story needs.
The last season was up and down, but did have some great moments. It's better to go out the Seinfeld route at your peak, than just hanging around long after you have ran out of ideas, a la Roseanne, Dallas, Friends.
Dean! Have you been shooting dope into your scrotum? You can tell me! I'm hip!