Personally, I don't think we should wallow in the grief of Rita's death for too long. If seasons of Dexter were 22 episodes long, then we might be able to spend some time on how Dexter deals with grief, considering he feels no emotions. But, we're already more than halfway through the season, I think 3 episodes is enough to deal with ending that chapter of his life.
I'm sure they wrote Astor and Cody out of the storyline because the actors were aging faster than the storyline progressing and honestly, kids always make a show worse. Do we REALLY want to see how Dexter manages 3 kids, a day job and his serial killer night life?? Sorry, I thought this show was about a serial killer who works in the crime lab. One of the themes of last season was Dexter wearing too many hats. . . this season they're correcting that.