When are You Justified In Buying a New/Like-New Car?

In an age of instant credit, negative savings rates and instant gratification, I ask when are you justified in buying a new/like-new car?

Joseph White wrote and article published in the Feb 28th Wall Street Journal’s Personal Finance section. It's titled "Cars Last Longer, Driving a Shift In All Aspects of the Auto Sector." It states that average service lives of vehicles (based on 2001 government data) are:

a) Cars: 13 years, 152k miles
b) Light Trucks (sport utilities, vans, trucks): 14 years, 180k miles

We have two 1998 model cars. One with 112k (Lexus) and mine with 121k (Acura). I'm trying to hold off on splurging. I'll probably wait till we exceed either the 13yr or 152k mile mark, then it's reasonable for us to buy a new/like-new car. The last car we had was a 1990 Celica GTS and was sold at 144.5k miles.

Cars are really the only thing I'm materialistic about. Oh, and the Lexus was bought used. Yeah, I'm ignoring the fact that some imports typically have longer than average service lives. Please be kind if you slam me for not being frugal enough.

Opinions?