^So the moral of this story is you're both smart men and good with your money.
I see both sides of the story.
I hate watching investments. Like going to the casino, except you never leave and the odds of winning small are better.
I also can see the advantage of making more with your money than you would by not spending it or by paying interest rates.
We're talking about car loans though, right? New cars in particular?
Interest in general on new cars has been and is still somewhere between fairly low and 0% for a long time. Most of the time anyways as long as you have good credit.
That said, I like paying cash for pretty much anything but a house. BUT, only because we're fortunate enough that it's possible for us to do that without significant financial impact. It may not be the absolute most you can make on your dollar, but it's nice knowing you owe nothing and have nothing at risk at the same time.