100K miles - what maintenance?

I think you're right in that driving a much older vehicle is cheaper than trading every few years. In Canada my experience has been that a full load diesel 1 ton ($73,000) depreciates about $4k per year for the first 5 years based on 20k miles per year. If after 20 years and 400,000 miles the vehicle is worthless it would depreciate an average of $3650 per year. So keeping my truck new has meant zero dollars on repairs and a few hundred per year above average for depreciation. There is the sales tax, the higher cost of insurance and the cost of borrowing (or lost opportunity cost if you pay cash) on the additional out lay of money that must be taken in to account but owning a newer truck isn't a tremendous amount more expensive than owning an older one.