Disneyof3: We have driven both ways many times. The 77/79 way is definately more challenging, but a very beautiful and interesting drive. The tunnels are really cool.
We have stopped in Mooresville, NC a few times, but we didn't even know it was a Nascar area - we don't follow it. The last time we stopped for a gift and we went to one of the museums and gift shops. It was pretty big. I would say it's very much worth a stop if you are fans. Here is a link:
http://www.racingontherocks.com/RaceCityUSA.htm
If you need to get to I-75 and Atlanta - just take I-85 at Charlotte NC. This is where I-85 and I-77 splits. It's about 3-4 hours to Atlanta from here.
If you like aquariums, you need to check out the brand new Georgia Aquarium. It just opened and is supposed to be great. Link:
http://www.georgiaaquarium.org/
Other things worth while to do while in Atlanta - not to worry the downtown area is fairly safe (same as Toronto) in the day. Also the area's these attractions are in are OK.
Zoo Atlanta is great - small and do-able in 3-4 hours.
http://www.zooatlanta.org/home.htm
World of Coke is also good and worth a visit:
http://www.woccatlanta.com/
They also give free samples!
If you are into history, the Jimmy Carter Presidential Library and Museum is also good and in the same area:
http://www.jimmycarterlibrary.org/
Another good aquarium along route I-75 is the Newport Aquarium in Newport, Kentucky just past the bridge over Cincinatti (south) It's another great smallish aquarium and we've been twice. It's in Dave Hunter's book Along I-75.
http://www.newportaquarium.com/ It would be a 3 or so hour stop and a great lunch break.
We've also been to the Tennesse Aquarium and found it just OK. It's off I-75 at Chattanooga TN.
Hope this helps and see you on the road!!