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.
It really needs to be known that Barcelona was the best team in the world more than 10 years ago and at that time there was really no team that could beat Barcelona with their tiki taka. But times have changed for now and Barcelona is not at the top, even I think Sevilla is still better than Barcelona if we compare their achievements in European competition. Barcelona has been left far behind by its rivals in European competition, namely Real Madrid, who have managed to be consistent in the Champions League and have often won the title. However, it must be admitted that for this season Manchester City is in control and no one is able to catch up to their achievements by winning the treble winner.