Normally, the submenus fly out to the right on a Spry vertical menu. They don't cover the remaining items. So there should be no need to move the other items down.
Are you testing the Spry menu on Internet Explorer? The Spry menus in the Dreamweaver Insert panel/bar are incompatible with IE 8 and IE 9. You need to insert a Spry Menu Bar 2.0 from the Adobe Widget Browser instead. There's a tutorial on Spry Menu Bar 2.0 at http://www.adobe.com/devnet/dreamweaver/articles/spry_menu_bar.html.
Just to complicate matters, I have been using the SpryMenuBar successfully for quite some time and have no problem with IE8 and IE9. The only problem is with touch screens because of their inability to show hover events.
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