"If you really want to be conservative with your car buying habits, restrict yourself to only paying cash and keep the vehicle for at least five years."
At least 5 years? Only 5? That doesn't make any sense without further guidelines. If all you do is buy used in cash (with no other limits) there are surely cases in which holding for 5 years will not be sufficient? Wierd advice. Shouldn't it have been more along the lines of, don't spend more than X% of your annual income on a car, then hold it for X years per $1000, or something. That kind of rule seems to have more application, IMO.
In another vein, though, I know MMM has a post about this but it didn't quite convince me. If you have the cash to purchase the car outright, why do you HAVE to use it? Wouldn't it be better to finance some of it at 1.9% or so if available and keep the rest of said cash invested for a higher return?