Hello Eric, sharing an OS Image between seperate WSM Installations is not supported. If you would patch the Image on one System, the other Server don't know about it and may run into incalculable issues. If the StreamingDir is located on a Network share, the WSM Server Services Need to run with the privileges of a user with full read/write permissions to the share. I recommend using WSM Service Credentials for this purpose. The WSM Sizing and Planning Guide covers this at page 25. Hope this helps! 
My original WSM server is 6.0 on a Win7 virtual machine.  The streaming directory is on a virtual hard drive in the same VM. For my next step, I took that virtual hard drive and shared it on the network. I am testing vWorkspace 7.2 on a Win 2k8 R2 VM.  I installed WSM 7.2 fine, but I tried to use the newly shared drive from my original WSM server to have access to the streaming images on the 7.2 server.  I get an error: 'Streaming directory is not be accessible. Please check the access permission / availability.' I tested accessing the folder via general browsing via explorer, am able to without issue.  My feeling is that WSM might have a problem with the store being on a network shared drive. Know a workaround or give me a hint to make this work?  I am trying to avoid having to setup a duplicate virtual hard drive on the SAN, which is short on space.  Thanks!
Mapped drive for Streaming directory for WSM?