Hi,

I stayed at the Hilton Barcelona ( Avenguda Diagonal) overnight before doing a BCN-LHR- HKG) .Whilst not exactly central it is close to the Maria Cristina metro stop L3 with a few minutes to the centre . Rooms were large and comfortable and the breakfast buffet was very good ( I was HH Gold at the time). I did not get lounge access but did not bother me.
Since then it looks like a Curio collection hotel ( Alexandra Barcelona) has opened near Passeig de Gracia and close to Pl Catalunya and the top end of La Rambla ( website suggests an outdoor pool and a spa)

Regards

TBS