You now have the Widget visibility settings available not only for default sudebars and sidebar replacements. But also for inserted sidebars in page/post content editor and template files.
In other words create a new sidebar using the Sidebar Widget Manager, insert it in any page template file or page/post content editor, go to Appearance -> Widgets, drop some widgets in the new sidebar, go to a specific widget and press the Set visibility button. In the popup you now have all visibility options available. If you want a widget hidden for a specific page make sure you dis-select this page from the Pages tab. Note that you also need to dis-select Pages from Template Hierarchy tab, since this means all pages and it has priority over the Pages tab.