Are disc brakes worth it? No, not really. I've been doing loaded touring in mountainous areas for 30+ years without them. A properly adjusted quality cantilever brake is more than enough to slow a touring load down from 50 mph. The problem is that most cantilevers aren't properly adjusted. I have mountain bike with them but even there a hub mounted disc brake doesn't stop any better than a properly adjusted rim brake.

The other problem with hub disc brakes and touring bikes is rack mounting. There are ways to mount them but most of them are kluge jobs at best. Perhaps racks will improve but a rim brake equipped touring bike is still about the best design for attaching racks and bags to a bike for loaded touring. The bugs have been worked out through years of development.