Not all cyclists dress as you say. I wore cycling shorts or bibs and regular cotton T-shirts when I was doing a lot of riding (up to 20 hours a week).
I generally were a helmet on most real rides, but I don't agree with the helmet Nazis. I never wore a helmet when riding my bike to school, something I did from elementary school on through high school. I raced a year in college and used my bike for all commuting (didn't have a car, mostly by choice). Helmets were not seen as a necessity in the 70s and early 80s. Helmets didn't really become popular until the lighter weight soft shell helmets (lycra covered, latter replaced by thin shells) came out in the 80s. Before then, there certainly wasn't an epidemic of head injuries/deaths from cycling. Sure if you look at the total cycling deaths in the USA, it comes out to something like 600-1000 per year. A negligible amount compared to things like car accidents.
As others have mentioned, multi-use paths are not good for training on the bike. They are only nice for cruising along slowly.