My personal opinion is that the new synthetic stuff has the old leather stuff beat to smithereens. The new stuff is weather resistant and still offers the same if not better protection than leather.
Beware of garage sale helmets is a good rule anyway. I would never buy a second hand helmet. I just wouldn't know for sure what kind of bump and bruise history the helmet has had.
I just finished my 2300 mile trip with the Joe Rocket mesh jacket and liner. No matter what the weather was, hot, chilly or rain, I was comfortable. Great piece of gear.