Are your parents still comfortable driving distances, esp into parts of the city where they don't live?
The two 'default' restaurants that come to mine, neither is newest nor cutting edge, but both started locally and have grown successfully locally are Puleo's and Aubreys. My In-Laws really liked the Aubrey's near them; to me it was ok and pretty good value for money.
Depending on a lot of variables, for a really special meal, dinner at BlackBerry Farm would cost hundreds and probably be the most memorable meal of their lives.
Up in Chilhowee Virginia, if they might like molecular gastronomy, Town House Grill would be the place.
A lot depends on your inlaws, my late FIL would put steak sauce on any beef that mooed, without tasting it. The latter two would have been totally wasted on him (heck, Ye Olde Steak House was almost a total waste on him.)
Ye Olde Steak House
6838 Chapman Hwy, Knoxville, TN 37920