Indeed. The Mail problem had been driving me mad for a couple of weeks or so now and I was focusing on threads that dealt with that - deleting Gmail account, turning off loading HTML images, deleting loads of emails in the hope that one was the trigger...
The Address book issue only came to my attention yesterday and I'd never have thought that that's where I should be looking to resolve Mail crashing...
A lucky break!
I'd like to add my voice to the chorus and also say that the outlined steps above solved my locked-up Contacts editing. Mine was in Mavericks and like many have stated, I'm not sure what event caused this to happen.
I had one little variation in the steps.
After step 2 was followed, there were still contacts listed upon launching the app.
I closed Contacts again and went one level deeper into:
Inside here I found another of the AddressBook-v22.abcddb files and deleted it. I also deleted the one found as in the instructions. Then upon reopening the Contacts app it was empty and everything else went as stated.