The only biggest benifit of switching to Mysql 5.6.5< is due to the feature that supports automatic failover utility which is default in Mysql 5.9.1 in a Mysql replication topology, this requires GTID level replication. Unless or until you don't really need an automatic failover within Mysql itself, we can work with the legacy features of Mysql 5.5 which is recognized most.
But also I would like to highlight some cons of using GTID:
A nontransactional storage engine (Myisam) mixed with updates to tables that use a transactional storage engine (Innodb) within the same transaction can result in multiple GTIDs being assigned to the same transaction. Thish might break sync between Master/Slave replication.
In a nut shell:
If your environment is stable in performance, High-availability and Security in your existing version it is better to keep untouched. If there is a necessity in any of the above then go for it. Management audit says a lot to keep latest version according to standards but they don't see technology wise what is standard? For this we need not spend time and effort to upgrade and sustain the same setup when it is feasible and effecient in current versions.