First of all:
1 - any Vue version reads older version files but can't read files saved by newer versions (e.g. v9 will read your v8 content but won't read v10 content);
2 - any Vue version writes files using it's specific version (you cannot tell v9 to create v8 compatible files).

To sum up, you go forward without problems but cannot go backward.

When I get a new version, I keep the old one on line for some time until I am rock sure that the new one is better; during this transition period, I keep separate directories for the different versions of files (e.g. a material directory called Own with a 9 and and a 9.5 directories in it until I remove v.9).

Content developers keep installed different versions of Vue to be able to save the different versions of files (you can have as many Vue versions installed as you like, just be careful of what you use).

Hope that it was clear, otherwise keep pestering.

GIMP 2.7.4, Inkscape 0.48, Genetica 3.6 Basic, FilterForge 3 Professional, Blender 2.61, SketchUp 8, PoserPro 2012, Vue 10 Infinite, World Machine 2.3, GeoControl 2