I find the titular question really intriguing, Paul. I've thought about it before, because I'm very interested in genealogy, and my dad (whose side of the family was less mapped and therefore more attractive to me!) is not. He says he can't imagine what importance the lives of ancestors he never met can have to him. I've convinced him this far, though: he acknowledges the people HE met that I never have gain importance for me through his stories!
I've mentioned my great-grandfather Frank, in the WWI thread: he was a wonderful formative influence on my dad. He taught him how to make things and fix things, instilled a lifelong tea habit (strong black tea with canned milk: very working-class Canadian), and let him drive his tractor when he still needed blocks tied *lengthwise* to his feet to hit the pedals. And Frank had an incredible life, which I know through Dad's stories and stories from Dad's mom, Frank's eldest child and best chum. He got to dandle my older sister on his knee -- we have a wonderful photo somewhere -- but died before I was born, and I am so sorry not to have even that unremembered connection my sister does.
I also know that my dad's great-grandfather John (Frank's father-in-law) was one of Dad's earliest babysitters, and a few childish memories Dad has from that. John's father fought in the Civil War! (For the Union -- he lived in one of the counties in Tennessee that seceded from the Confederacy, so he nipped across the border and joined a Kentucky regiment.) To me, that's very meaningful: that by word of mouth, I am that closely connected to history that old. It's better when we have stories about them than when they're just photographs.
So yes, like you, when I only have photographs, I pore over them for clues. One of the wonderful things with genealogy is that I can get more clues, and read into them too: working out from ages on ship manifests, for instance, that my mom's great-grandfather came over to the US with his dad and worked before they could arrange for his mom and younger siblings to join them, at the tail end of the Potato Famine. It means something, to see how young my ancestors married or how young they emigrated -- how young they had to work. I spent a long time trying to find a census record for that Irish immigrant ancestor's wife after the one where she was a widow with five kids. I finally realized I lost her because she remarried -- to a widower, also Irish, with a bunch of kids of his own. And I wonder, how much was affection, how much convenience and survival? There are a hundred stories in these photos and facts, if you try.