Speaking of Vince, I would have expected more hestitation on his part against "ratting out" Dexter as the jealous husband to Quinn, who Vince should realize isn't Dexter's friend and is not the right person to confide in.
Vince is essentially saying he thinks Dex murdered Rita; that isn't something you just babble randomly. If Vince really thinks that, he needs to go to LaGuerta. If he isn't willing to do that, he should have the sense to stfu. Starting a rumor that he isn't willing to follow through on, about someone who's always been his friend, seems to be too pointlessly malicious to fit Vince's persona.
I know it was a plot convenience, but the writers should have made more of an effort to create a plausible scenario: Vince lets Deb in on his suspicions, Deb of course shoots it down, Quinn overhears; Vince is drunk; or some other mitigating factor.