Let's take their example. They want to go from a four door car to a minivan. The cheapest one in my area after tax, tag, and title is going to run them at least $20,000, which is pretty cheap for a brand new vehicle (Dodge). That vehicle is going to depreciate at around $2,000 a year until it gets down to around $5,000. The first year depreciation alone will be enough to overhaul an engine. Even if they put an entirely new transmission and engine into their old vehicle it would only take them 3 years to recoup the cost compared to the 3 years of depreciation. The maintenance cost will defintiely be less since it's under warranty, but they're definitely going to spend more on gas and insurance as well.
My ex-girlfriend made this same mistake, except hers was twice as severe. She had a VW and was tired of paying for things to get fixed at the dealership. There's another lesson, don't go to the dealership, they rip you off more than anybody. So instead she decided it was a good idea to trade her car in on a lease! How fucking stupid is that?! Unless you own a business leasing a vehicle is probably the most expensive form of transportation! Don't do it!!! I don't know why she broke up with me...