You can only use the xp:text to render HTML, not to inject XPages xp:tags into the source XML. Remember that the XML "source" you place into the source pane of the XPage is interpreted and converted into a .java file, then compiled to a .class for execution on the server at design time. The XML tree is not re-parsed at run time. If you have finalized HTML, then you can use the xp:text...
You are going to have to "preplan" where you want to dynamically include content, then place the xp:include tags where you want to include content, then compute the which page to load at run time. You can use the rendered and loaded attributes of the xp:include tag to turn on or off the rendering of a specific xp:include as well.