The purpose of this issue is to keep track of all toolbar problems found:
[ ] Hide some menu items on folder_contents view (#1475)
[ ] User should know easily who is logged in (#962)
[ ] Not immediate way to know if an item has expired using the toolbar (#1577)
[ ] Don't change button contents on hover (#1610)
We've noticed these problems as well. We ended up going with a toolbar on top and bottom. There is just no way to fit everything you need on the toolbar otherwise.
Here is an example:

Then you also have more room to have breadcrumbs and other things in the toolbar.
I think that part of the problem here is that plugin authors don't have much options with regard to where to make their items available on the toolbar. Greenbar/toolbar tabs has always been easiest. But from a UX perspective this is not ideal. Not everything is top level and needs to be one click away. For example, in that list Sydication, aliases, Analytics and even history I think wouldn't be used often enough.
I think we can do a few things
I mostly agree with vanhgheem and djay here. After using Plone 5 in various sites in the last months, I agree that there's room for improvement, even though I do like Plone 5 and its new toolbar very much. Right now I'm working on a site that has 11 links on the toolbar - and they all look as important compared to each other.

It doesn't or shouldn't have to be major changes - just make the most important links bold (Add, Edit, Contents) and put some horizontal lines and/or marging to separate primary and secondary function sets.

A more radical change could be a new "More..." or "Settings" -menu item that could contain not so frequently used functions such as Rules, Sharing, History and others that come from add ons.
Most helpful comment
We've noticed these problems as well. We ended up going with a toolbar on top and bottom. There is just no way to fit everything you need on the toolbar otherwise.
Here is an example:
Then you also have more room to have breadcrumbs and other things in the toolbar.