Though have ridden bikes in the past without a radiator guard without issue, I figured I would put one on my wrr just in case.
I've gotten some dings in my guard already, so its doing something!
Popular choice for Rear is a Dunlop d606.
I went to the New England Classic Charity trail ride a couple weekends ago and saw a lot of bikes running a Pirelli MT 43. Its a trials tire.