Changing text with a click event: how to restore default state of text in jQuery if/else statement
as a first step I would rewrite the last if statement

else if ((clicked =! "Text1") &amp;&amp; (clicked != "Text2") &amp;&amp; (clicked != "Text3") ) 
    {
        $("#ActText, #AdaptText, #PlanText").css("opacity", "1");  // return to default state
    } 


After that you could rewrite it as a switch statement: http://www.w3schools.com/js/js_switch.asp 

edit : this would be better...

var textArray = new Array("Text1","Text2","Text3");
if($.inArray(clicked,textArray){
    $("#Text2, #Text3").css("opacity", "1");
}
else {
 $("#" + clicked).css("opacity", "0.2");
}