My Robaix does not have fs or discs. It is a great bike and geometry works for an older neck like mine. It barely fits 28's though, in fact I put a 25 on the front as clearance is too tight with a 28. I've ridden distances on it frequently. .
got the Diverge because we travel and camp a lot and never know what surface I'll be riding on so fatter tires and discs were appropriate. Also it has a 48/30 crank which is nice and allows me to stay in the big chainring longer. I'd choose the Diverge for a century ride, just is softer. Keep in mind, I ride solo and a century takes me close to 7 hours, so I'm not breaking any speed records.
Value is relative, it is the most I've ever spent on a bike. IMO, 105's are what Ultegra was and there's not much harm there. I'm planning on keeping it for a long time. I think I've finally got 2 good bikes for any conditions.