You are spot on with your comments. There is no need for you to upgrade to version 10 if you don't need them. That's why VMware is now calling it VM Compatibility level rather than Virtual Hardware. This is to remove the pressure from always trying to keep up with the virtual hardware.
From experience, I find upgrading Virtual Hardware one of the scariest part of any upgrade project. Ive encountered lots of issue after it that's why it is always recommended to create a snapshot before doing a virtual hardware upgrade. Its the only way to rollback.