Whether or not a clean start with a new environment is neccesary is entirely up to the customer.
That being said, you should consider that private keys are likely stored on the old keyserver, and those private keys are likely neccesary to access data.
I highly recommend reviewing the migration article, and consider what features are used in your environment vs what you would be using on a PGP Universal Server (now known as Symantec Encryption Management Server)
Migrating from Keyserver 7.x to PGP Universal Server - http://www.symantec.com/docs/TECH149856
If you do not believe you need the data that the migration recommends exporting, then perhaps you can do a fresh start with SEMS.
A little about SEMS :
SEMS is an appliance like linux based server. It is standalone, and requires its own server.
Many people set it up as as virtual machine with VMWARE.
For information on how SEMS should be setup with VMWARE see the following link :
Best Practices for Creating a New Virtual Machine for Symantec Encryption Management Server - http://www.symantec.com/docs/TECH186060