well
i would rather put my belief on Espinoza, Samper, Calvet... or any other youngster we have at Barca B..
maybe im naive
i don't know how good they are or how good they will become
take somebody like montoya, i don't see him being an word class fullback belonging to the best 3 in the world at that postion. Not now, nor in 3-4 years. When Alves is 33-34 u need a replacement and use Montoya as a decent sub.
Bartra imo should be able to become as good as pique or puyol.
Montoya is good enough for 80% of la liga games, still that is not good enough when you want the CL.
sergi could become world class or 'just' a very decent barca squad member. we don't know yet but Gundogan definitely will become one of the best at his position.
now you can buy him, wait another 2 years and he'll be somewhere in England.