Restaurants off the top of my head which are "unique:

1. Lambert's Cafe - Ozark, MO (NOTE: No credit cards, always crowded, plan to wait).
The Travel Channel ranked them as the "World's Best Place to Pig Out".

2. Big Texan - Amarillo, TX

Both these would fall right in to your dinnertime. It's about 9 hours from Chicago to Ozark and from Ozark to Amarillo. The Big Texan also has a motel on premises and I even got a free breakfast buffet with the room when I stayed there. It was ranked as #10 on the same Best Places to Pig Out show.

A shortcut to Phoenix from I-40: Get off at Holbrook, take AZ-77/377/277/260 to Payson, then AZ-87 to Phoenix. This cuts off 40 miles and is very scenic.