Lyon to St Remy - recommended stops

I would recommend Orange, to visit the theater and adjacent museum. It is very close to the A7 motorway, so no time wasted.
Another option is the Cité du Chocolat - Valhrona in Tain l'Hermitage, which is a rather pretty town on the banks of the Rhône.
And if you are in the mood for cute villages, la Garde Adhémar and Saint Paul Trois Châteaux fit the bill and are close to the main highway.

If you have any interest in Roman history in France, set aside time to visit Vienne. It was an important trading port in Roman Gaul and the ruins there still are in the process of being discovered. It has a fascinating museum, a place to visit in-place ruins in the open air (with ongoing excavations in places), a forum, and a Roman temple tucked into a town square.

We didn't know the temple was there and were quite surprised to stumble across it as we looked for a tabac where we could buy our timbres fiscaux to update our residency cards. That was in the pre-electronic timbres fiscaux days.

Thanks for the suggestions!