Include tags should either be within PHP or SHTML files, not HTML files. See here on how to use php includes: http://www.tizag.com/phpT/include.php
On a sidenote, Spry has been deprecated and is no longer officially supported or actively developed by Adobe: http://blogs.adobe.com/dreamweaver/2012/08/update-on-adobe-spry-framework-availability.htm l
You may want to consider using a pure CSS or jQuery menu. Lots of them are available here: http://www.freshdesignweb.com/jquery-menu.html
10 Templates is far too many for one project. You should be using 1 or maybe 2 templates maximum for site wide structure. Add embedded CSS code for page specific styles.
Use Server-Side Includes for site wide menus. If your web host doesn't support SSI, find a better host.
CSS Menu Systems
Project Seven Responsive Tabs
Pop-Menu Magic2 by PVII (DW extension purchase)
CSS3 Dropdown Menus