When we went from 7 to 8 I had to spend time adjusting my custom theme. I’d like to know up front if I’ll have to do that again after installing 8.2. If so, I’ll put it off until I have more time.
I personally haven’t noticed really any differences from V8 - 8.2 in Themes other than some fixes etc in Themes. However I would suggest to backup first via “Menu / Backup” just incase you need to restore.