Sanctuary only stops your hand, in this case hand size, being altered when its not your turn. Owning a Sanct in play does not stop you from increasing your own hand size.
As to it not being particually strong i did originally have upped as +2 hand space for 2 quanta and unupped as +2 hand space for 3 quanta but i felt that made the upped version too strong as it could be played from 1 SN