Just a little anecdotal evidence on this. I was ferrying a bike down to my mechanic, who is less than four miles away late in the season (November, as I recall.) It was very cold, so I dressed up in full gear. I'd been somewhat casual about it at times that season. The bike was running like crap, as it needed the carbs adjusted, so I wasn't going very fast. I hit a frost patch on the road and took a tumble at around 30 mph.
My boots saved my feet, my gloves saved my hands, and the armored textile riding pants saved my "gentleman's tackle." I did not hit my head or my helmet.
I walked away with a jammed thumb and a few other bumps and bruises. I wrote off the boots and pants -- about $400 worth of gear. The pants were brand-new a week prior. The heel on my right boot had a deep slash in it, and a nasty cut by the toe. These weren't even full-on boots, just a pair of workman-style lace ups. The pavement wore a hole through the fabric of the pants right near my crotch, but the liner saved the manly bits.
Considering that getting just a few stitches would have cost double what I had in the gear, I've been far more religious about things since. My "casual" riding boot is once again a pair of tall workman-style leather lace-ups, which is as light as I'll go. My serious touring boots are a pair of Aerostich CTBs, and I keep two pair of motocross boots for the trails. They are not fashionable. They can be a PITA to take on and off. The MX boots are a bitch to walk in. They help with control of the bike, however, and I consider them as necessary as a good helmet.