"Experts agree", spanish is so easy for an english speaker to learn, that you will certainly be seen as "less than bright" at best (if not flat-out ignorant, arrogant, and anti-social) if you can't at least begin pick it up after a couple of months.
You will prabably learn castillian (and the dialect local to wherever you choose to settle) very quickly if, as you suggest, you avoid the narrow and deathly boring world of the "coastie ghettos" (the racial/cultural stress of foreigners desperatly trying to recreate their home cultures in Spain is sad and repulsive), and instead go for something interesting in the "real world". Good luck!

By the way, contrary to the case in "other cultures", the spaniard will always warm up to the foreigner who demonstrates an interest in learning spanish - and your blunders or accent will almost always be seen as endearing before they ever offend. You can't lose!
(Besides the working-class job, be sure to consider the barstool after the workday is done to be a classroom as well.)
Of course, as happens anywhere, a person percieved as unwilling to learn to the local lingua is written-off (sometimes politely, sometimes not).