Nice guide Jake.
One small change I would make though would be to add a guest conditional, so the tab doesn't show up if not logged in.
That can be achieved with the following:
HTML:
<xen:if is="{$visitor.user_id}">
<li class="navTab PopupClosed"><a href="{xen:link account/upgrades}" class="navLink">{xen:phrase account_upgrades}</a></li>
</xen:if>