I was disappointed to see that overrides in symbols only apply to content, basically CMS without using CMS, which is nice...
...but, I think it would be truly useful if you could also apply stylistic, or at the very least visibility overrides.
For example, I created a left side menu to organize my clients products in different ways. The main shop page has a larger photo driven version of the "Shop by Jewelry Type" menu, that sits at the top of the left side menu. While I need this menu on every other page, it's obviously redundant on this page.
I know that I can disconnect this instance from the symbol and delete it, but then any time I change the menu, I have to replace it with the symbol and delete the redundant menu. Not a big deal in this case, but in a situation that's more complex, or has many overrides for many pages, it could become easy to forget everything you need to do each time you make a change.