How to justify the 5DMKIII?

I have seen lots of people saying its not worth the extra, ie in the UK its almost twice the price of the MKII.

As I understand it's the AF that's the main advantage, however there are a few others tweaks, like better higher ISO, HDR, etc.

Shooting at lower ISO shows not difference in IQ v MKII, correct?

However for non pro's how did you justify the cost and has anyone had buyer remorse.

Ian