Why would Sam want the Impala?

Because she's the Impala!

Seriously, it was more of an "I don't need you" message that was stacked on all the others he had given Dean by that point. I understand all the possible reasons, I just think it hurt Dean's feelings.

But Sam is my darling too--so I'm waiting to see what are behind his reasons.

I still hold that taking the impala would have been too painful and too detrimental to the detachment he has achieved.

Good point.

I know what Theresa means -- Sam wouldn't want the Impala, but for Dean to offer and be blown off so casually had to hurt. The Impala means the world to him, and helped save the world (which we, at least, know, given Sam's reaction to it in Swan Song), and I think the whole purpose of the scene was to point out that Sam has changed.

What Julie said. He's defining himself as a separate person, and the Impala doesn't play into that at all. It was entirely consistent with his characterisation up to that point, and way less puzzling to me than the expression on his face during the hug.

Dean completely can't comprehend this (and is no doubt hurt--but he's so fixated on Sam that even normal independence hurts him), but then again, Sam can't comprehend Dean being willing to stay now that he knows. So there's disconnect on both sides.

The hurtful thing was not Sam turning down the Impala, but turning it down so coldly and casually. Something wrong PTSD, a deal, turned evil, not Sam - something.

I'd be very surprised if Show decided Dean had thirty years of torture and ten years of torturing and could still look relieved and almost happy and Sammy had hours or days and couldn't manage the same. I doubt they'll ever draw such a huge distinction between their emotional capabilities.

Another difference is Dean was hugging Sam very soon after his emergence from the grave, so his responses were still very raw. Sam's reunion with Dean was new to Dean, but Sam had been back among the living for a year and had seen Dean from a distance, and perhaps had even been keeping tabs on him. His emotions weren't being bombarded the same way Dean's were.

I want to say it's horrendously flashy, but seriously, I've just become overused to the Impala. It's not like they've been crawling around subtly all this time.

From a purely non-emotional, practical perspective: the Impala gets crappy gas mileage. From what I could find when Googling, it gets somewhere between 16-19 miles per gallon. It's more and more difficult to find replacement parts. And it makes it easier for any law enforcement agency seeking a Winchester to spot the driver.

WANT MOAR NOW!

We can talk about aired previews right? The one that aired right after SPN.

When the kids are singing the lullaby in the background, it made me think of the SPN con episode with the hookman saying something like, "yeah, how original. Supernatural bringing in more creepy children"

the Impala gets crappy gas mileage.

I wondered if this was why Dean wasn't driving it. More of the suburban conversion in play.

but turning it down so coldly and casually. Something wrong PTSD, a deal, turned evil, not Sam - something.

He's been back a year! Dean hasn't had time to deal, but it's a long time for him to come to terms with their separation. But then again, I didn't see it as cold. Calm, yes. Clear, yes. Not cold.

I wondered if this was why Dean wasn't driving it.

From the fact that Dean didn't outright get rid of the car, or the leather jacket and the journal, and the way he looked at the jacket . . . I think he put aside almost all the trappings of his past except for what was smart and practical. and by his reaction to the jacket, it's a painful reminder of his old life. His old life that included Sam.

And he can't let those reminders go, and he also can't stand the daily visual reminders. And so I think his offer to Sam of the impala is a way to give it life again without involving himself. But I think it's just as hard for Sam. The car represents something the neither of them have anymore.