I worked at a bike shop briefly in summer of 2011, and there was some model Trek upright bike with a Shimano 7 speed hub. I don't remember if it had a chain or a belt. The drivetrain felt very friction-free. I've ridden a belt-driven bike and didn't notice anything bad about it. Was it possible the belt was misaligned or something?

I can feel a little friction in first gear in an old AW hub, but not enough to make it a deal breaker. My guess is modern IGHs are even better than that.

As for ease of roadside repairs, it depends on how good you are. An old English 3-speed is easy for me but not for everyone. If I had a bike with a full chaincase, though, I would put a very heavy tire on the rear, because then the job gets pretty bad.