I stayed in Santander on a study abroad trip last summer. I remember of all the places I went in Europe, Spain was probably top for places I wouldn't want to ride. Driving is a full contact sport there!

Have fun though. That's a beautiful area. The N-625 through the Picos de Europa is a nice road, but it's the opposite way from where you're going.
You are going to scare him ,ja,ja

I think it's not a dead risk to ride in Spain. Yes, there are some dangerous people but you can find this kind of people in all places.
Maybe in some cities people are more aggressive but specially since the drive license is based on Point System people are more careful and respectful.
It could be better, but Spain is not the worst place in Europe to ride, for sure!!