Nostalgia sounds relatively harmless even like something to indulge in with a modicum of comfort, until we examine the two Greek root words that form nostalgia: Boston, meaning "returning home" and altos, meaning "pain." (Brene Brown, Rising Strong)
How many church meetings have you attended when someone has said, "I remember when we would (fill in the blank) and there were so many people who came to church."? Or, "It used to be expected that people would attend worship - or bring their children to worship." While I think there is a benefit to examining what we have done in the past, I think dwelling on our history is not constructive.
UNLESS we see the second Greek word in nostalgia - altos, meaning pain. Do we see the pain in our past? Do we recognize the mistakes we have made, and the consequences those mistakes have had on our present? Do we ever, as a church, look at our past and ask, "What mistakes did we make in the past? How do we do it differently now?"
"There's nothing wrong with celebrating the good things in our past. But memories, like witnesses, do not always tell the truth, the whole truth , and nothing but the truth. We need to cross examine them..." (Stephanie Coontz, as quoted in Rising Strong)