You bring up intresting points. I think the writers do pay some attention to the fans because destiel, and wincest were mention on the show as well as ep 200th, it was more of a tribute to the fans
However, I do not like the fact that Charlie, Jo, and Jo's mom died the way they did I felt their characters could have had a more lasting impact on the show.
I am not sure about Castiel's death, I am sure fans will revolt especially Destiel/Castiel fans. I remeber the time he died but came back due to fan demand.
I spend a lot of time analyzing shows/books, its more of a hobby than anything. I