As for mingling different sorts of traffic - I've heard of several spots here in the Netherlands where they've done just that, and it doesn't always result in lower accident rates. At some point you cross the line between "less of a comfort zone everybody is more aware" and "confusing mess that has so many things going on that nobody is aware of everything".
A narrow road can still be predictable - you'll have to be alert to prevent minor bumps, but there's no surprises that can result in rear-ends because you have to slam on the brakes.
I don't have any studies numbers to back it up atm.
My town has in the past year eliminated raised sidewalks/pavements. All that happens now in those areas is that cars drive all over the pedestrian bits and park on them. It's called a "shared space" but car drivers, being rather selfish, just drive and park wherever they wish with scant regard for pedestrians.
I don't have any studies numbers to back it up atm.