Having to manually update Google+ is a serious negative for its use:
volunteer time is a very precious resource. Simply because other groups
(most of which have paid employees) are doing it doesn't mean that every
group ought to invest its limited resources in doing so. It's not a
popular site, it's resource-intensive to maintain, and most of the target
audience on Google+ is also present on at least one of the other locations
that are regularly being maintained. I'd not consider it a priority.
Risker/Anne