We went to Chattanooga last April and enjoyed ourselves.
We took the kids to the aquarium, but honestly, I would have enjoyed it even without the kids. There are two parts and I found the fresh water tanks particularly interesting.
If you like Civil War history, check out Chickamauga National Battlefield, just over the border into Georgia, but just a few miles outside of Chattanooga. My kids hated Chickamauga but I'd like to go back someday to check it out at a more leisurely pace. You can also go up to Point Park on Lookout Mountain. Not necessary to pay for a train ride, just drive up your truck to the end of the road, that's that national park.
Enjoy