I bet good ol'UK won't swap miles for km any time soon, Gill. Miles are easy, yards are something else completely. Most of the times, you don't need to change anything, Vue converts everything for you, but when it comes to mixed materials, or large scale materials, it may come in screwed up at the new size. And Mark, I suggest you don't change anything in 7.4, it will either come up well in 8, or just resave the material in 8 if it isn't converted right.
A problem can arise if you are creating content for Vue7 and up, I had this with my Hibiscus I sell at Corn. For some reason, the materials looked a lot better in Vue7 at 0.1 already , and for this reason, they were loaded at 0.01 in Vue 8 (which is logical), but didn't look good at such a small size. Then there isn't much you can do, except a readme asking the user to change material sizes in Vue8 manually, which isn't very nice.