Hi Nick!,
I think you hit the nail on the head when you wrote:
Obviously, if anyone had no reason to be re-baptized (see my other post on this), no body of elders in their sane mind (do they have one after all?) would ever accept to go annually through that process and even less allow the person to be actually re-baptized!
The PO in that congregation was a somewhat bizzare fellow named Keith Krieger. Small rural congregations often develop unusual habits and look with suspicion on outsiders (shocked by it as I was at the time, I can relate much weirder tales than multiple baptism).
How I became aware of it was that, whilst witnessing the baptisms at Ridgehaven Assembly Hall (in Adelaide's north eastern suburbs) I noticed this brother (can't think of his name at the mo) in line to be dunked. Keith's son Ashley (a fellow pioneer and ministerial servant) was standing next to me and I asked the dub equivalent of wtf's going on? Ashly laughed, said it was alright and explained the history. Apparently this brother kept re-presenting to Keith with a guilty conscience over something or other and Keith had him "re-do the questions" in prep for a re-dunk. At the time I joked he was just doing it for the applause (this never went down well with him or his supporters who gushed and love bombed like they'd done time and time before). Another strange tale but true from the congregation the Watchtower forgot.