God, I wish someone would clue in Showtime that the reason the ratings are up is because the show is finally aiming towards a real finale (with huge stakes and revelations along the way), and people want to see how it all ends up.
The only way I could possibly go for an additional season is if it follows Dexter on the run from the law, and completely gets away from the usual characters and settings.
But if it's just more of the same, boring Miami PD crap, then hell no.
This would seem like a plausible explanation of the ratings. Finding out what finally happens is indeed why I read Dexter threads, although the show is too unbearably bad by comparison with the first couple of seasons to tolerate watching.
Except that the ratings, while quite good for cable, were never so large, so the number of fans tuning back in probably wouldn't provide that much of a bump. I fear that more people actually like the Dexter who always gets away with killing, no matter how far-fetched the escape, while having some beautiful women obsessing over him.