Natural thing about software is that you enhance it, thus you create next versions of it. How do you handle that in concern of Spotfire ?
At least two ways I can think of.
First, in 7.5 and above you can spin up a test node and copy down any dxp you want from live to develop in test. Once the "upgrade" or changes are complete you then would backup the live version to disk somewhere... anywhere you do other backups, and deploy the new version to live.
For pre-7.5 the idea is the same but you would have to create a test folder in live with restricted access to test your upgrade on a web player.
Strictly speaking of "what version are you on" in regards to Analytics like there is in software isn't really the same in my opinion. There should only be one version of the truth. If you are to run multiple versions you'd have to manage their updates separately for caching which is cumbersome in my opinion. Also, realizing the analytic has a GUID which relates to its information sources means that running them in parallel in the same environment will cause duplication.
If this isn't what you were shooting for I'd love for you to elaborate on the original post and clarify anything I assumed. Cheers mate.
EDIT
Regarding the changes in 7.5, see this article from Tibco starting on p.42 which explains that Spotfire has a new topology with a service oriented architecture. In 7.5 onward, IIS is no longer used and to access the web player you doesn't even go to the "web server" anymore. The application server handles all access and is the central point for authentication and management.