We stayed at a camp site not too far from La Peineta the last time Springsteen played there so I can't tell you about hotels, but I can tell you that we had no problems getting the metro after the concert.
A lot of people came on coaches and in cars, but even with thousands of people using the metro afterwards the queues moved really quickly and we were away within twenty minutes of the end of the show.
Enjoy it. It will be a great concert. I've got tickets for the Barcelona show on 17th May and can't wait!