No, I'd not give a thought as to changing my travel plans to Spain for Sept/Oct. Of course, we are mainly doing a 2 week road trip, so public transportation will be used to a minimum in our case. Still, I have no qualms about using the public transportation anywhere in Spain while there.
When I traveled to Israel years back my friends could not understand how I could visit a country where terrorism could take my life. I admit, that trip made me a bit nervous. However, I also learned a valuable lesson there - life goes on, and one cannot live in fear of "what if". Take necessary cautions as needed, certainly. But enjoy life always!