Hi and welcome,
Here's a possible route to get you from Indy to Sparta and then onto Bowling Green:
In the small town of Greensburg, IN, there's a little restaurant on the town square called "Stories." It's where many locals go and has good ol' Midwestern comfort food.
On top of the court house across the street from Stories is a tree that's been growing out of the tower since the 1800's.
Or, if you wanted to drive a little farther down I-74 to Oldenburg (about 3 miles north of the Interstate), there are two restaurants that are known for their fried chicken: Wagner's Village Inn and The Brauhaus. Wagner's is pan-fried with a lot of pepper, so it takes a while to prepare. You can't go wrong with either. (I used to live in nearby Batesville for 17 years.)
In Batesville, there's a nice little restaurant called Lil' Charlie's with a more contemporary menu and their own brewed beer.
Across the Ohio River from Spara in Florence, IN is Belterra Casino, a place to stay(?) (I've not been there, so I can't tell you anything about it.)
I know it's the same weekend as the race, but Cincinnati has it's Oktoberfest that weekend as well. (Cincinnati has a large German heritage and it is the largest Oktoberfest in the US.)
Hope that helps with your planning.