Is there any SharePointDesigner2010 add-in to use SPD more effectively? Also, can I use Visual Studio like SharePointDesigner to edit pages and list views? Is there any VS add-in for this or not?
No, there aren't plugin for SP Designer and there aren't plugin for VS to edit pages and list view as Designer does.
The explanation is simple the two tools have two different focus. Designer is not for developer users instead VS is for developers that want customize heavily SharePoint.