Benefits of updating - well, since we are up to version 18.60 (vs. your 5.31) there is the matter of support because any programatic fixes that may come about would require it. Given that your rig is on XP, the newer versions are not going to be compatible.
If everything is working well still and you are happy with it, then don't upgrade. There are a number of users over the years that have gotten things set "just right" and disconnected their machines from the internet.
There are many of them that have had to come back because something breaks requiring them to upgrade because their kit is running an on an out of support OS, drivers, GPU, etc. for the new parts. Typically it is a hard drive or an arcade monitor or mainboard components that have to be replaced.
There are - so long as Tom supports the software - always newer features and capabilities and even derivitive versions of GameEx.
Wish I could say more. Back up what you can and plan for a future upgrade.