I'm old enough to remember when canvas/cotton duck was still a common material for panniers and bags. Carradice bags look great when creating a classic look for a bike. But IMO it is more show than go. In the real world a weekend of rain will make you wonder HTF anyone ever toured with these before synthetic bags came along.
I would also caution against going overboard with the "classic" look. I made the mistake of using Brooks leather bar tape on my last tour. The tape has absolutely no padding. I had numb hands for 5 weeks. There's also good things to be said about some of the "modern" stuff.