While I agree there is no reason for anyone not to immigrate, or get on marvellously with the people in a new country, what I find surprising is that you seem to believe you will have as much in common with Spanish people in general as they would among each other.
Yes, they have great regional and educational variations and one societal group there may not share much in common with another, but still there is likely to be a barrier between you and them unless you have lived there most of your life and are completely fluent in Spanish and very widely read. Even then there will be a trace of ‘other’.
Just as there will most likely be some feelings of distinction and otherness between one region and another, there would be an even greater degree of this between a ‘Spaniard’ ( not Basque) in general and a non Spaniard.
This not to say you might not be welcomed with open arms!