for now, barcelona is one of the clubs with the best squad in the world so if they intend to buy players again, it's just a waste. What Xavi has to do right now is focus on making the current squad work very effectively. they must be able to at least win a domestic trophy in the following season and the UCL is one of the trophies that Barcelona must target.
The best in the world 
I think Barcelona is only the best team in La Liga not in the world because the best team in the world for the season that has ended is the English team that won the UCL two days ago. So how can you say that Barcelona is the best team in the world if Barcelona still failed in the UCL and have to try again next season. After all, the nickname of the best team in the world is a team that can get three trophies like what Manchester City got this past season. Not just one trophy, namely in La Liga.