I've been fortunate to have visited Spain many times due to the blessing that my wife's sister lives in Madrid. Spain is wonderful, and there is so much more to do and see than the Costa del Sol and Marbella.
As with any trip worth taking, some prior reading and DVD viewing of materials from the library will make a visit to Spain much more rewarding. Books and movies of travel advice, factual histories and fiction (particularly Hemingway's) will allow you to make your trip twice: once at home and again on the turf.
Hemingway's "For Whom the Bell Tolls" is a great novel, one of the 20th century's best. It doesn't have his finest prose, but the plot and his balanced account of the Spanish Civil War make it superb reading and a good preparation for your travels.
If you want to know more about the Spanish Civil War (and you should; that conflict is far from over in the hearts of Spaniards), take a look at "Ghosts of Spain: Travels Through Spain and Its Silent Past." In that factual account, Giles Tremlett details the still-bitter controversy over the years of Franco's rule and the ways in which, to this day, Fascists' murders, secret burials and a lingering hatred between the Left and the Right poisons community.
An aside: For several years, El Valle de los Caidos - The Valley of the Fallen - was a popular tourist site. Franco built a huge basilica, using prisoners of war, in honor of the Fascists killed in the civil war and, ultimately, as a monument to himself. The building is larger than St. Peter's in Rome and at one time had a funicular that carried the faithful up to a gigantic concrete cross atop a high peak. All has changed in recent years. The funicular doesn't work. There have been large boulders tumbling from the cross' mount. The bookstore is closed. And the staff has been greatly reduced. Only two buses a day take the curious few from the incredible monastery and palace, El Escorial, up the hilly way to Franco's deteriorating pile.
Other suggestions for those interested in the period's history and in Spain's broader history include the movies "Pan's Labyrinth" and Bradley Smith's "Spain: A History in Art."
Plan to see more of Spain than just Barcelona or Madrid, essential as they are for any extended visit. Recently we took a week's trip through Northern Spain's Cantabrian coastal region. The Picos de Europa (high mountains that come close to rivaling Summit County's peaks), the Guggenheim museum in Bilbao, the lovely beaches in Ribadesilla and San Sebastian, the seafood, the Basque language and the cooler weather in summer all make the trip a pleasure.
Particularly good guides are Dana Facaros' "Northern Spain," "Back Roads of Spain," and "Hiking in Spain." Yes, by all means take some good walking shoes. Who knows, perhaps you'll join the pilgrims and say, "Yo soy pelegrino, a Santiago me voy!"