My two cents if you haven't already bought your ticket is to fly into Madrid instead and take the train to Seville. Flying all the way to the far side of Spain only to then fly all the way back across seems a little much. And you also have the risk of a late arrival into BCN and a very expensive re-ticketing/hotel on the later/next day Vueling flight. On a separate ticket arriving from Delta, they have absolutely no obligation to re-accommodate you and in the peak season, who knows, there could be no availability for re-booking for days if flights are full. With the train option, if you miss you train, you can change to any other for a penalty of I think only 10%. Or rent a car, or whatever. Because of the proximity of Madrid and Seville, you'd have more options. You can get from Madrid's airport to the main train station by metro easily.