Springfield, MO is actually on the great Mother Road, route 66!
You might also try some Route 66 sites.
Some places that were recommended to us when we did our Route 66 trip were:
Aunt Martha’s Pancake House is an institution, right off of Glenstone
(recommended numerous times to us, but we didn't end up eating in Springfield at all, got in too late, etc.)
There is also a Lamberts-Home of Throwed rolls in Springfield.(waits can be long)
On the way to Springfield:
Richland, Missouri - Caveman Bar-BQ & Steak House
inside a cave 50 feet above the road. It is in an old resort.
26880 Rochester Rd Richland, MO 65556 573-765-4554
This place sounded intriguing, but in researching it, I saw mixed reviews - It is also CASH ONLY-another good website for researching more causal joints to eat is roadfood.com
"If you reject the food, ignore the customs, fear the religion and avoid the people, you might better stay home."
~James Michener