When only some things have icons, it's almost like a flag that these things are more special/useful/used. I think that is by far more useful than everything having an icon that you have to think about (or see the text next to it) to understand
I think this is a useful pattern, but I'm not convinced that having specific distinct icons for menu items to highlight them as important is useful. Presentation order and/or simply a consistent difference in presentation for the highlighted items makes more sense.
Some things are only occasionally what you are looking for, and making them require a full scan of every menu entry is fine.
The thoughtful inclusion and exclusion of icons in menu items builds hierarchy. When every item is special, none are. You've lost the ability to differentiate.
Icons everywhere is a hallmark to me of "webby" UI.