Bug 80833 [Import/Export] Import exisiting should pre-check for project already in workspace
While it is good that it lets you import projects in the default workspace location, it should not let you select projects that already exist in the workspace (since importing such a project will fail). When searching for .project files in the file system, it could use IWorkspaceRoot.findFilesForLocation followed by checking IFile.exists() to filter out .project files for existing projects.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/wizards/datatransfer/WizardProjectsImportPage.java
ILeveledImportStructureProvider provider;
		/**
		 * Create a record for a project based on the info in the file.
		 * 
		 * @param file
		 */
		ProjectRecord(File file) {
			projectSystemFile = file;
			setProjectName();
		}
		/**
		 * @param file
		 *            The Object representing the .project file
		 * @param parent
		 *            The parent folder of the .project file
		 * @param level
		 *            The number of levels deep in the provider the file is
		 * @param entryProvider
		 *            The provider for the archive file that contains it
		 */
		ProjectRecord(Object file, Object parent, int level,
				ILeveledImportStructureProvider entryProvider) {
			this.projectArchiveFile = file;
			this.parent = parent;
			this.level = level;
			this.provider = entryProvider;
			setProjectName();
		}
		/**
		 * Set the name of the project based on the projectFile.