There is a process that is being traversed through this rebuild. To me, the Braves have to look critically at the current team and decide where it is and is it on track for where they want to be. If you look at this team and decide that it is at best a 70 win team, then adding one expensive bat isn't going to make it a contender. At best what you get is a 75 win team. It doesn't move the needle enough. What it does do is change the team from a last place or near last place team to a more middle of the pack team where there are much less advantages available for a rebuilding team such as draft position, draft pool dollars, rule 5 position, international pool dollar, competitive balance picks, even revenue sharing. So, while it is a bit counter intuitive, it's clear that becoming mediocre is worse for a franchise under the current MLB rules than being dead last. The exception to that is where a team becomes mediocre a year before becoming great, a natural progression of talent.
So, you have to ask yourself if you think the Braves as currently constructed both at the ML level and at the minor league pipeline is on the cusp of greatness. Do they have the talent in the pipeline to develop into a sustained competitor? Or, do they still have a lot of work to do?
To me, that answer is easy. The Braves have virtually 0 power and production bats outside of Freeman (and Freeman is not a classic power and production 1B at this time). You have a 31-32 yo rookie prospect who is out of position for LF who may or may not hit for enough power and production to be considered as slightly below average. After that, it gets really thin. Cespedes, a 30 yo, coming off a career year, who biologically is entering the decline phase of his career, would have to replace either the aforementioned 31 yo rookie OR displace our light hitting veteran OF in RF who is costing 11M per year.
Does adding Cespedes make this an 85 win team (not good enough to actually WIN anything but good enough to make everyone feel a little better?) I guess you can never say never since the Mets might all get the debilitating clap and they might get it from the Nats and the M's might take a three hour tour and end up on Gilligan's island. But, in reality, no this team isn't one player away from being an 85 win team.
So why tie up limited capital if it serves no strategic purpose?