That's basically what i'm saying
But I think it's more important to keep someone like Bobby around because it keeps things grounded.
Like Xander in Buffy in a way.
You've got this series full of angels and demons and even sam and dean have their fair share of weird and wonderful quirks... Bobby is the 'everyman' in a sense. The guy who brings the Winchesters back down to earth, reminds them what it's like to be human.
Cas, while being a great supporting character who I miss a lot, is not as important to me as Bobby because he doesn't provide that function.