Repair costs for an Audi can be easily as high as those for a BMW or Mercedes.
The Infiniti is a fine car. My only concern is that you might find the ride overly firm. The G37 will be far more powerful than you require. One of its strenghts is handling, which you don't care about. Since you're in Chicago, you might want all-wheel-drive. Fuel economy won't be good, if this is at all a concern.
Among Acuras, I'd suggest a look at the TSX. It's a little more compact than the Infiniti, and could be better-suited to your needs.
One car that probably isn't on your radar at all, but that is worth checking out, is the Buick Verano. It's about the size of the Acura. Rear seat room is a weakness, but it doesn't sound like you have much need for it. Buick offers the larger Regal, but I'm a little less sure of its reliability (avoid the 2011).
New a Verano with Leather Package listed for just over $27,000. It looks like you can get a 2012 or even a 2013 with about 20,000 miles for about $15,000.
My main concern is whether you'd find the Verano roomy enough, but you'll be able to determine this through a test drive.