They look great on the Riders that have them. They were designed with 'em, they should keep them and if you took them away, it wouldn't look right.
The Riders that don't have one don't need one. They were designed without 'em, giving them one would not automatically improve anything.
But I would like to see another new Rider with one, some day. One that had been designed with having a scarf in mind. Cuz I do love me the scarves (I would betray my country for a female Rider with a scarf. )
The scarves where an inventive little way of giving the hero the style of a cape while being less potentially cumbersome. (besides it fits better for a bike riding hero anyway.)