I think the cost of owning an old square should be divided into two parts: maintenance and repair.
Maintenance is: tires, brakes, alignment, oil/filter changes, battery, wiper blades, light bulbs, wash and wax, paint touch up, etc.
Repair is: everything else that breaks.
Maintenance will be done on any vehicle - new or old. Repairs will be done more often on old vehicles. If you buy a new vehicle you will have 3 years or 36,000 miles of no repair cost. If you take good care of that new vehicle you will have low repair costs for years more. When repairs are needed on newer vehicles the repair cost is more, so I would be inclined to trade the new vehicle in or sell it after 3 years.
If you wait until your old square breaks down and then fix it, then the repair cost per year will be low. If you keep everything in top mechanical shape, then your repair cost per year will be high - until you have repaired/replaced everything.
