Thiago was mismanaged because he was promoted and he did not see a clear ascending trend in his role for the team. In fact, he had an ascending trend under Guardiola, that halted and went backwards under Tito.
Xavi does probably have a couple of seasons left, but if someone like Gundogan comes next summer, he would certainly assume the starting role over Xavi, who would still feature heavily in the team, but at a reduced role more fitting for his current physical limitations.
So supposing you buy Gundogan next summer in this scenario, and keep Samper another year in Barca B until he is 20. Gundogan could start, play over 50 games, while Xavi could still be featured to a lesser extend and play around 40.
Then, in the 2015-2016 season, you could promote Samper, reduce Xavi's role further as he would be entering 36 years of age, and you could see a split of Gundogan still featuring over 50 games as your starter, but now Xavi and Samper would share the 40.
By the 2016-2017 season, Xavi is close to 37 and possibly retiring, Gundogan is still your starter for the 3rd year, but now Samper is his full backup (if he merits it) and is only 22-23 years old still, featuring in over 40 games.
That's an ascending trend for Samper as he matures, and you can then evaluate if he merits being pushed ahead of Gundogan for an undisputed starter.
You also take care of the present needs of the team, without harming its future.