There is a nice map of the Paradores in Ian's link. The Paradores along the east coast in your route are not that great or historically significant. The best are the ones on your way back to Madrid from San Sebastian.
Check out Santo Domingo de la Calzada: "The hotel occupies a former 12th-century hospital near the cathedral, erected by St. Dominic to take in pilgrims traveling on the Way of St. James."
and Siguenza: "The Parador de Sigüenza is an imposing medieval castle situated in an Arab fortress built atop a Roman settlement"
