Coincidentally, we had a second visit from immigration just the last week, not from the main Hat Yai immigration office but from the office in Sadao. This I was told had nothing to do with my extension, which I'd collected a couple weeks before, rather they said their task was to check on the validity of marriages; checking for fake marriages. All very polite, a few photographs, some questions, sign a document saying we're married witnessed by someone not a family member.
So this may become a regular thing?
I still don't think the extension and 90 day reporting procedures are particularly arduous, I've lived and worked in a lot of countries and I don't find Thailand's rules to be especially difficult. Certainly it's no prison, I have a passport and I can leave whenever I wish.