Despite Dexter's not-so-healthy relationship with Vogel, he still felt a connection to her - she surpassed the role of "spiritual" mother and became a real mother figure for Dexter. We can see how her death has altered him, especially as he kneels next to her lifeless body and says, "The last time I was in a pool of my mother's blood, I was too young to do anything about it, but I'm no longer a child." Killing Saxon will no longer be just for protection, but for vengeance.
Aside from a final kill, Dexter needs to prepare to pack up his whole life and sell whatever's left. Jamie comments on seeing Dexter's apartment so bare and packed up: "Seeing your place all boxed up is making this so real." This mirrors the audience's sentiments exactly - it's hard to believe there's just one episode left in the series; one last chance for this final season to redeem itself.
For a psychopath who is supposed to feel no empathy, Dexter is starting to show real emotion. While he was showing his boat to a potential buyer, we detected a hint of sadness from Dex. And for a man who spent his entire life pretending, at the very end, we learn he's not pretending anymore. During his impromptu going away party at Batista's restaurant, Debra tells Dexter he should pretend like he's going to miss the Miami Metro gang, to which he narrates, "It's no longer pretend." Dexter even tells Quinn he approves of his relationship with Deb! That's major change.
One slightly hilarious bit of irony regarding Dex's going away festivities: it was held after Vogel's funeral. Seems oddly fitting for a serial killer.