Having done the trip to / from central IL as well as Austin to Indy all of them several times...Get down to Indy take 70 to St. Louis, Personally I take 255 around St Louis, then 44 across MO and OK (note 44 through OK is the Turnpike and is a toll road) to IH 35. 35 south using 35E through Dallas to 45 south.
I generally prefer interstates for long drives so this influences my driving habits a bit also.
As noted there are not a huge number of tourist items in Houston, NASA being the larger one. That being said Houston is the 4th largest city in the country and you can pretty much find most anything to do here.
The is a museum district, theater district, Buffalo Bayou for an outdoor park walking strip in the city, Minute Maid park, Astrodome, and the coastal areas for Galveston, and Kema.
Anyway I currently live in Houston if you need something let me know.
-Robert