I drive the dog urine out of my truck. Currently at 315k miles. It's a 2005.
I maintain it well, preventatively, and as needed with an open budget. I do it all myself after work.
I run the numbers before any repair to make sure that I would not be better off, cost-wise, to be looking at a new or newer truck. Maintaining my current truck wins by a mile even when faced with expensive repairs. I have never been down more than a week, and that was working on replacing the heads and head gaskets everyday when I got off work, a job that requires pulling the cab off of my truck.
A professional mechanic would have had that job done in one day, possibly two. I would sure like to think that a municipality employs a mechanic or three, no?
Based on cost, I have a hard time buying any argument presented. Based on "need" or reliability, it becomes a less concrete-facts kind of argument and one more based on emotion or opinion, so it is probably not one worth having.
Let me edit to add that I understand you partially agree based on buying a better quality vehicle up front versus saving some money and having to replace it, but I would make the argument that you should not need to replace either version near as frequently as it appears most departments do.