I don't know how long you've been on 6.3 SP1, but from a software perspective, this release is ancient.
You may find that your release is pretty stable for those functions that you are using. However, there have been many hotfixes through the years, and the dependency chain of hotfixes has grown uncomfortably long. Should you run into an issue, even if there is an existing hotfix, you may find it unacceptably risky to take a change that might (for example) introduce over a hundred dependent hotfixes; it might take you a very long time to validate all those changes, and/or find and integrate those changes with custom versions of the rules which you already are using.
That said, upgrading to 7.2 is like replacing your 1963 Ford with a '72 Impala. If you're going to go through the pain of upgrading, come into the 21st century with 8.1!!