I also stayed with Carrara 8 for a while, mostly because I was irritated that DAZ charged for the V8 upgrade while promising the updated documentation "Very Soon". So I bought it, then waited several years and got no updated docs. Then DAZ wanted more money for 8.5, which apparently was primarily for Genesis compatibility, something I have no interest in. Eventually the upgrade price got very low for a few days, so I bought it ... still just the C7 docs, and I think that's still true today. Other than that, I have had no real problems with v 8.5, but just a few advantages, like some timeline features. But you'll have to dig around the website for how they work ... and from what I've tried, the Genesis stuff can be a problem also.

If Carrara V8 is working for you, I'd only recommend paying for 8.5 if it is VERY cheap. I seriously doubt there will ever be a V9, but V8/8.5 work fine for me and I use it on a daily basis. Here is an animation that people seem to like:

https://www.youtube.com/watch?v=Dxcbh71VUlg