Planning to rent a car and drive from Ghent to Bastogne and back in a BIG day.
Wondering if there's a route worth detouring to take or stick to the shortest route?

Our current goal is to visit the 101st Museum & the War Museum & see if time allows for anything else.
Suggestions for anything else in the area that we could see?

I don't know the area that well, but looking at the map Dinant or La Roche en Ardennes would be an option.
But these places suffered during the recent floods. The Bastogne area was affected too. For when is this?

Gent is busy during rush hour, and there are some extensive roadworks now. The ring road around Brussels is terrible at all times, but avoid the morning and evening rush hours. Looking at the map google shows the fastest route going north around Brussels. The loop south may be better, traffic-wise.

We will be there Sept 22. Has the flooding caused any closures? Detours?

We won't be driving in Gent at all, just leaving & returning to the car rental agency, but if leaving early may hit Brussels at the wrong time.
Is the Waze app commonly used in Europe? or stick with Google directions?

I think Liege was the most damaged on your route from the floods. Looks like a 2.5 hour ride. My Dad was part of the 82nd at the Battle. They were the 509th, a bastard battalion that liked being that but when attached it was the 82nd. He jumped into North Africa so the Bulge was his last battle. They came from outside of Paris on the back of a truck with lightweight jackets. We spent three nights there and still could have used more time. Now you are making me want to revisit. So hoping we get to Belgium in November.
I bet your car will have GPS.

Use Waze or Google to get an estimate of driving times. Check a few times at the time of day you want to leave.
It's quiet at the moment, since schools don't go back until September 1st.

There have been road closures and bridges collapsing, houses collapsing, hopefully that will have cleared up by September. Don't count on it though, this is Belgium.

Roadworks in Gent are on the ring road outside the city, but mostly on the road to Antwerp, as far as I know.

I agree with Dinant and La-Roche-en-Ardennes and would add Bouillon to that, but all these places are on rivers. I know the Semois (the river through Bouillon) was flooded quite badly. Have a look for the carved walking stick shop in La-Roche-en-Ardennes. There are also a few stops in the area where beer is brewed (such as Chimay), but if you want to visit the monastery you have to book in ahead.

If you run out of time I would prioritise Dinant out of those. It is easy to drive through and get a glimpse of the town, but you only get the beautiful view from the opposite side of the river to the town, so don't miss that.

Lavandula