We have removed access to Ideas for the moment. However, if a user goes the "+" icon they can still add an idea. They add an idea and then they cannot actually access it. If a navigation item is removed, it should be removed from the "+" icon as well.
Whilst I am expressing this for "Ideas", this should be relayed fr every entity where you can remove the display of it, show remove the display of creating a new item of that type in the "+" drop down as well.