People are different. Take a photo of someone and from that point on it only increases in value. Look back at it in an hour and it brings back the feelings of the day; look back at it in a month and it brings early stages of nostalgia; look back at it in a year and it might bring you to tears. And obviously that’s not the case with every portrait, but they have that potential.
And you aren’t mining anything, you aren’t taking anything from the moment. It’s the closest thing to cheating the second law and something I find pays dividends on the daily.
You can’t create anything more valuable with anything less than you can with a photograph.