I second the Biarritz recommendation. While I fell in love with the various Spanish and Basque regions and cultures on the
Camino Frances, I would have loved to experience French-Basque culture more, had I the time. I flew into Biarritz and it pained me to leave so fast.
Visiting Biarritz is at the top of my list for the next Camino. Since my first Camino, I've seen much of southern France (amazing). French seafood is off the charts, and by all accounts Biarritz is an epicenter for it. I have seen excellent reviews for the Musée Asiatica, which has an extensive collection of Asian art.
If you choose Biarritz, please post about it after your Camino -- I would love to hear about it from someone who has experienced it.
Post Script: Yes, St.-Jean-Pied-de-Port is easily seen in a few hours. But I got into town in the early afternoon and would have loved to have had more time exploring the church (pilgrim Mass!), the restaurants, and bakeries (food is quite the driver for me, if you couldn't tell already!). The energy, anticipation and pilgrim vibe is intense, so it really is a special place. Try to get at least a half a day to experience it if you can.