VMware Fusion through version 3.x, version 4 doesn't have this issue, when copied to a new system by Migration Assistant needs to be uninstalled/reinstalled by its installer for it to function properly because the Migration Assistant does not in all cases get everything correct with the complexities of the VMware Fusion application! This just is not a big deal and take about 5 minutes, not counting the time to download it if you don't already have the installer, so just do it! Uninstalling/reinstalling VMware Fusion does not remove the Virtual Machines just like uninstalling/reinstalling Microsoft Office it doesn't remove the Word documents or Excel workbooks, etc. So just copy/move the Virtual Machine Package from one location to the other or system to the other by whatever means you want, Migration Assistant included. As far as anything in the Virtual Machine, OS, Applications and or User Data it's all there and no need to reinstall anything other then VMware Fusion itself as the Virtual Machine Package is analogous to the document created by Word, it's the work product of the application and can be copied/moved around independent of the application that created it and contains whatever have been placed in it, so to speak.
Migration Assistant doesn't always get all of the Permissions correct on what it migrates and prior to version 4 not all of the application was stored in the Application Bundle and was spread out it in four different locations, not counting what was created under each users account. VMware recommends uninstalling/reinstalling VMware Fusion when copied/moved by the Migration Assistant however with version 4 everything, not counting what was created under each users account, is now in the Application Bundle, not spread out and one of the components that routinely broke is no longer in version 4.
Since you already have a license for VMware Fusion 2.x I'd at least give it a try on the new system and if all is fine and it does what you need it to do then why purchase the upgrade. You can always try 3.x or 4.x for free with the free 30 day trial serial number and see what you think. Do make a proper manual backup of the Virtual Machine Package before upgrading between major versions, just in case.