I travel a lot and I now always get comprehensive travel insurance. Thankfully I have not had to use it, but my parents have in a big way, and if they didn't have medical coverage they would be short many thousands of dollars.
A good place to shop for travel insurance is
http://www.insuremytrip.com/ I've noticed, though, that it's a good idea to visit the web pages of the individual companies, because insuremytrip doesn't always have all the available policies. Still, it's a good place to start with comparisons.
I've been getting TravelGuard's Protect Assist coverage. It's one of the few that covers everything, including medical and trip cancellation/interruption when due to terrorism. It's expensive, though.
As for the clinics in Spain, my experiences during the 13 years I lived there were almost all positive - and with two kids, I went often! My opinion of health services in Spain is very high. I wouldn't hesitate to get medical help there whenever necessary.