north through France or south through Portugal?

It is a long drive to Paris from Santiago de Compostela, about 900 miles. Doable in your time frame, but if you remain in Iberia I think you will have more time to visit those sites and towns that appeal to you. Also check rental car costs for dropping car off in France. If you start in Santiago and return it to Sevilla you will not incur those costs. I am going to suggest a few places to visit for the Portugal/Spain route. As you drive south from Santiago into Portugal there are many quaint fishing towns along the way. A few suggestions for Portugal include the little town of Obidos, The fishing and seaside town of Nazaré, Tomar with its Knights Templar history, and Evora with its Roman ruins. Lisbon also has many interesting sites and I found Lisbon to have a very unique feel to it but it may be too much of a big city ambience. As you cross over into Spain, visit Mérida. The Roman ruins there are extensive and impressive but Mérida itself is much more modern than quaint. You might consider remaining in Spain. There are many places that fit your description between Santiago and Sevilla. If you have never been to Salamanca you should stop there. It is a bigger city but the architecture in its historical quarter is beautiful. You could stop in the town of Plasencia. I have not been there yet but it is on my wish list of places in Spain to visit. Look at photos. I think it matches exactly what you are looking for. Cáceres is wonderful. You can spend hours wandering the old medieval streets. The little town of Trujillo also offers what you describe. It looks much the same as it did hundreds of years ago. Another favorite is the town of Guadalupe, very pretty. Leave yourself several days to explore Sevilla. Lots to see there. A side trip to Córdoba is also doable. If you have the car, right outside of Córdoba are the ruins of Medina Azahara.

Back in '03, I visited Evora, Coimbra, and Lisbon - was expecting to like the smaller places much better, but wound up being totally smitten by Lisbon. Gorgeous, amazing place, and also a great base for day trips.

Have to agree that visiting Portugal, with its many small historic towns, is your best bet. If you're driving from Santiago you can also stop at Porto and perhaps drive a bit along the Douro. You could stay in Nazare. We often use it as a base to visit Coimbra with one of the oldest universities (1290) in continuous operation, the Roman ruins of Conimbriga, the medieval monastery of Alcobaca, Batalha monastery, the beautiful walled town of Obidos, and others. From Lisbon you can also visit Sintra with its many palaces. If you continue driving to Seville, as was previously suggested, you could also visit Evora and the beautiful, historic towns of Monsaraz, Serpa, and Mertola with their medieval houses and/or castles. This is more than you can actually do in your 10 days but if you research these towns you can pick those that appeal to you. Have a great trip!

I think it is interesting that you all suggested heading south rather than taking the northern route. We are thrilled. Portugal has been on our bucket list and we have been to France several times.
Thank you for all your suggestions.