Watching a restoration crew in Charleston flipped my view on old wood

I was helping fix a porch on a house from the 1800s, and the lead guy pulled me aside when I went to cut out a bad board. He said, 'Hold up, let's see if it's just the surface.' We spent an hour with a card scraper and some citristrip, and under all that grime and paint was perfect heart pine. I mean, I always figured old, dark wood was just rotten or too far gone. Now I try to salvage first on any job over fifty years old. How do you guys decide when to replace versus restore?