Have you considered Madrid at all as your base? I think it meets your "authenticity" point better than BCN. Admittedly, Madrid has no beach but it is (i) a vibrant city way less touristy than BCN; and (ii) it also has plenty of UNESCO world heritage sites within a 2h drive. Examples: Segovia, El Escoria, Cuenca, Toledo..
I am a Spaniard myself so I can vouch for that. Although I was born in Madrid so clearly biased here
