I'm also thinking of her conversation with Sam near the end, when Sam wonders why his mother would have sacrificed and Missouri says, "Well, to protect her boys, of course." As far was we know, Missouri has no children, but this line makes me wonder what experiences, if any, she might have with the parent-child bond. Right now I'm going with the idea that she is infertile - that she wanted to be a mother, but was unable to conceive.
2. In Asylum, as in Wendigo, Sam and Dean let a civilian or civilians stay with them on the hunt because the civilian is concerned about a loved one (as Dean says in Wendigo: "Her brother's missing, Sam. She's not gonna just sit this out."). It's a contrast to Dean in particular's disapproving attitude towards Jo in No Exit. There are two significant differences here: Jo is out to be a hunter, not just concerned about a loved one in one hunt. Also, Jo has a mother who is vehemently opposed to her going on any hunt. Nonetheless, it's an interesting difference in attitude - especially since Jo is obviously more qualified than the civilians in Wendigo and Asylum.
I suspect it has to do with where Dean is in season one - thinking that questioning John makes one a bad son - versus questioning everything about John after his death in early season two.
3. Scarecrow is a big turning point episode for both brothers: Sam chooses his connection to Dean over his vengeance quest, while Dean sincerely gives his blessing for Sam to leave, admitting admiration. A far cry from Dead in the Water, when he pulled rank as the good son to convince Sam to go on a hunt.
I don't think it's a coincidence that this occurs right after Sam's possessed verbal and physical assault on Dean in Asylum. It's clear that Dean was not 100% convinced by Sam's claim he did not mean it. It just seems odd to me - that hearing Sam say such cruel things seems to have led to Dean being more open about his admiration for Sam's rebelliousness.