When listing events, I noticed dublicate SQL's for getting number of visitors. This is because the getMembersCount function is called twice. This was present in v3 and now also in v4. In v4 this is found in layouts/events/list.php

<a href="<?php echo $event->getGuestLink(
COMMUNITY_EVENT_STATUS_ATTEND
); ?>"><?php echo JText::sprintf(
(!CStringHelper::isSingular(
$event->getMembersCount(COMMUNITY_EVENT_STATUS_ATTEND)
)) ? 'COM_COMMUNITY_EVENTS_ATTANDEE_COUNT_MANY_NUMBER' : 'COM_COMMUNITY_EVENTS_ATTANDEE_COUNT_NUMBER',
$event->getMembersCount(COMMUNITY_EVENT_STATUS_ATTEND)
); ?></a>

You right, please you change to be like this :

<?php $attendCount = $event->getMembersCount(COMMUNITY_EVENT_STATUS_ATTEND)?>
<a href="<?php echo $event->getGuestLink(COMMUNITY_EVENT_STATUS_ATTEND); ?>"><?php echo JText::sprintf(
(!CStringHelper::isSingular($attendCount)) ? 'COM_COMMUNITY_EVENTS_ATTANDEE_COUNT_MANY_NUMBER' : 'COM_COMMUNITY_EVENTS_ATTANDEE_COUNT_NUMBER',$attendCount); ?></a>