Just buy it, BUT:

Have your wife test drive it for more than a few miles. Maybe even rent whatever her choice of car is over a weekend to make darn sure that's really what she wants.

I was in the same boat as you a couple years ago. It was time for a new ride, and I was prepared to pay cash. Wait to talk to the dealership before you tell them you're gonna pay cash. They offered me a 4 year, 0% loan, which (for me) was a no-brainer. Interest rates are almost nothing...just something to consider.