Would you say that the harder an event is to recreate, the more nostalgic we feel about it?

I have speculated this for a number of years. There have been places from my past that I have been able to return to, but once they are destroyed (for development, or whatever) I suddenly start to feel nostalgic about them and remember good times there. Similar with people - there are old friends that I have not thought about much for years, but I hear that they have died and suddenly I think about them often and remember good times fondly.

Yeah. That's normal.
What is also normal is to look back on events and people and your own actions with rose-tinted glasses.
If we had perfect autobiographic memory - our mistakes and losses might cripple us, disable that vital optimism one needs to go on, and prevent us from forgiving ourselves and others. It's also easy to think, you still have time to maybe reactivate a friendship, write them an e-mail, but never do it, postponing it endlessly. When it's too late one day, it hurts a lot.