I don't feel like the appearance of the Samulet and Kevin were emotional manipulation so much as the writers trying to wrap up loose ends that fans have consistently asked about. They've been doing a lot of that this season, with some mediocre results and some good ones. Earlier on we got resolution (not great resolution, mind you) for the rift between Sam and Dean in Season 8, which is something I constantly saw fans ask for/about. And Dean has had multiple opportunities to show how much he cares for Sam now that the mark is off his arm, which is the only apology the writers will probably ever give us for "it should have been you up there." The Samulet exists to point out the presence of God; it's pretty much done everything it could do. And Kevin never did get a good final resolution - last we saw he was a ghost - and with all the shit he went through for being a prophet of Chuck, sending him to Heaven was the least Chuck could do for him. I mean, he *could* return him to life, but with Amara on the loose, that might not feel like too much of a reward.

Frankly, I wouldn't be surprised (hell, I'd be pleased) if the writers resolve Michael & Adam, too. Although... that might be hoping for too much.