It has been (I realised today) over 2 and a half years since I paid Nong Khai Immigration a visit. In light of what the Captain said above I decided to pay them a visit this morning. I did not particularly want to go to Vientiane so just wanted a 30 extension to my tourist visa which expires tomorrow.
Got there reasonably early (8:45) but they were open, even if I was their first customer of the day.
Well what an amazing turn around in attitude over that time...
Just the 3 lady officers present when I arrived, all smiled, all returned my swadee khap. Showed me where extension form was, dealt with it efficiently & pleasantly (slight hiccup in that they originally gave me a 60 day extension rather than 30 & so had to amend it).
Charged me 1,900 baht for the extension & 10 baht for all the passport copying - I had copied nothing

As the captain says above, completed form, passport photo, passport & exit slip & a few copies of passport pages are all that are required.
My Happy came in to take his position just as I was exiting.
One other thing I noted was that the 3 officers also said hello & goodbye to my TG, although she did not actually accompany me to the desk just into the room - the last time I went she was treated little better than dirt when she was trying to help with some Thai/English translation.
All in all a very quick & surprisingly pleasant experience & just about one of the best for politeness & service that I have encountered anywhere in the world with officials...