I really doubt everything came together just because Baez was a cancer and all the young players suddenly felt better after he was gone. They were already starting to play better before he went on the IL. They did even better after he left, because they got his terrible bat out of the line-up and added some other players who had been in the minors or were hurt. If they acquired Bregman or Alonso and they hit, they would help the team. If they didn't hit, they would not help the team.
The run they have been on since August 10 has been amazing, but I don't believe they are as good as their record during that span. If they came back with the same group next year, I don't believe they would do as well. At the same time, I do think they are pretty close to being a team that can be a perennial contender and it seems like the the right time to start spending. I do think they need another good bat, which could come from free agency or trade. They also need at another starter and a couple of relievers. I hope they try to acquire all of those things this off-season.