I totally get the argument for getting AC+ for mobile devices as you say - the physical abuse they might undertake - but sometimes the issue is internal / build quality (as per your PowerBook), and that's why I picked up AC+ for my Mini M2. In fact, my original AC+ just lapsed, and I've extended the Plan with a small yearly charge.
Though unrelated to AC+ (because it was still under the original 1 year warranty) my iPhone 16 recently packed it in. Internals fried (not the result of external abuse) - Apple unable to repair - so I was given a brand new phone the day I took the 16 in. If it wasn't under warranty / AC+ - and had they been able to repair it - that would have been a $750 repair. Had they not, I would have been looking at buying a new phone.
There's no telling what may be happening internally. Yes, with luck, most faults will show themselves within first year, but as a desktop (and Apple) device, its likely it will be held onto longer than most - so no guarantee when /if your Mini will need repair. As long as AC+ remains cheaper than trade-in value of device, I'm okay with the expense.