Getting a visa is not that hard. Spain is also really relaxed about immigration.
If you are in the tech industry, many startups and big companies (e.g. Facebook, Google) have offices in Madrid and Barcelona.
If you wanna do remote work, the Canary Islands might be soon offering a special visa and a low tax regime.
You could also try a digital nomad lifestyle. If you return to the US every now and then, it should be fine.