Your <?php return bp_loggedin_user_domain() ?>
is part of a string therefor it is not executed. You should probably have
'<li class="myclass"><a href="'. bp_loggedin_user_domain() .'activity/just-me/">My Wall</a> ...
Your <?php return bp_loggedin_user_domain() ?>
is part of a string therefor it is not executed. You should probably have
'<li class="myclass"><a href="'. bp_loggedin_user_domain() .'activity/just-me/">My Wall</a> ...