What a coincidence, my wife and I just got back from a 1 week trip to Nashville!
Yes, Loveless Cafe is a must. We enjoyed it so much that we went once for dinner and again for breakfast. We ate the smoked boneless pork loin with peach preserves and the smoked turkey with cranberry BBQ sauce for dinner. The fried chicken is supposed to be legendary. Prices are low ($13 for a huge entree) and the desserts are great, especially the banana pudding and coconut pie. They have a great gift shop called Hams and Jams where you can buy some country ham, bacon, sausage, preserves and sorghum syrup to take home. The drive out there is quite beautiful too.
A Nashville-only specialty is the hot chicken. The best purveyor by far is Prince's at 123 Ewing Drive, but it is NOT centrally located. This is truly a dive. If that bothers you, just get take-out like we sometimes do. Mild is somewhat hot, Medium is plenty hot and Hot is incendiary. Only order Extra Hot if you're crazy. I think the best deal there is the breast w/wing for $5 as they're huge and come with 2 slices of white bread to sop up the greasy hot glaze and pickles too. I think the sides are a ripoff at $2 for a little coleslaw or potato salad, but the fries are good.
If you prefer to stay in the downtown area, there is another joint called 400 degrees that also serves great hot chicken at 390 Peabody St. We had some of theirs at the Hot Chicken Festival on July 4 and it was tasty.
Puckett's Grocery and Restaurant at 500 Church Street (also downtown) is a fun joint with awesome chicken fried steak and great burgers. As a bonus, beers on tap including the excellent local Yazoo are 1/2 price during happy hour.
There really isn't great BBQ in Nashville, that's more of a Memphis thing.
For a more upscale restaurant, there is the nationally recognized Catbird Seat. The 7-course tasting menu is $100. Given what you said about your Dad, though, the Capitol Grille in the Hermitage Hotel downtown might be a better choice. It's fine dining, updated southern-style, and most of the menu is very approachable but still pricey.
If you're a country music lover the Country Music Hall of Fame is right downtown as is the Ryman Auditorium. We toured the CMHOF during the day and went to a bluegrass concert at the Ryman at night. Great fun!
I don't agree about the whole Opryland thing, it's a cultural wasteland IMHO.
I already mentioned some foodstuffs to take home from Loveless. The CMHOF gift store carries the excellent Olive & Sinclair Southern Artisan Chocolate bars, you might want to buy a few as they are superb. If you're not going to the CMHOF, the HG Hill Urban Market at 415 Church St. and Puckett's has them too. Midtown Wine & Spirits is near downtown at 1610 Church Street and carries many Tennessee spirits beyond Jack Daniels like the Nashville-made Collier and McKeel whiskey and even some artisan moonshine!
Another interesting place to visit is Hatch Show Print at 316 Broadway (Downtown). It is an old letterpress and they print many of the concert bills, some of which you can buy as souvenirs.
I hope this helps you out!