Include Letchworth State Park when en route. Take some time to visit the Corning Glass Museum in Corning.
We have always stayed in Corning rather than Watkins Glen. It’s an easy drive to the track. However, I consider the current hotel rates in Corning to be an outrage. Horseheads seems to be a bit more reasonable. Pick your poison!
We always go to the Market St Brewing Co. and Restaurant on the main street one night for dinner. There are plenty of alternatives along the Corning main street.
From 390 cut east at Wayland across to Branchport on Keuka Lake. There is a nice run down the western side of the lake to Hammondsport. Dine at the Village Inn, food and Beer are great. You can then take the back roads to Watkins Glen or Corning or cut down to Bath and re-join 390/86 to Corning.
I can also recommend the “Marmalade Cat” B&B in Watkins Glen as a place to stay.
Lots of wineries and craft breweries in the Keuka & Seneca Lake areas if that floats your boat. I have visited Keuka Lake a number of times and there are plenty of places to visit. A possible accommodation location is the Esperanza Mansion in Branchport: http://www.esperanzamansion.com/ overlooking the lake.
There is the Curtiss Aviation Museum in Hammondsport. Also lots happening in the area: http://www.keukalake.com/