I don't think there is any gap between the NH and the SH now. There is a gap between NZ and the rest but even that is narrowing. If I had to rank teams now I'd say England, Ireland and Scotland would all beat Oz and SA more times then they would lose to them.
The Saffa's are in a mess and its not just rugby its the same in Cricket, there are some serious structural problems in SA sport that make Welsh rugby problems look tiny. I also think Oz have been talked up too much. Sure they beat NZ but only in a dead rubber when the tournament was over and they are certainly better then the team that both the Lions and England beat over there, but I'm not having it that they're all that.
I don't see why not if the comparison to England post WC winners is to hold. If you spend all your time and effort focusing on the squad you have it'll take at least 6 years to fix the mess that occurs when the inevitable retirements come around. This is where Ireland have been so effective as they seem to have managed this better than most.